ICYMI: Prospector Demonstration Video

At work, Bill Bolton has been working on a movie of our Prospector demonstration (with enough annotations and captions to understand what is going on). I’ll be doing a more detailed blog post on the Altius Space Machines website sometime this week, but wanted to provide this for those who don’t follow me on twitter.

The music for this was done by Kevin MacLeod of incompetech.com. Kevin has done a lot of music pieces for Kerbal Space Program, and offered to do us a custom piece for free since he thought what we were doing was so cool. As he put it, the music gets a bit epic near the end, “But you’re picking a freaking boulder up off an asteroid–it should be epic!”

Posted in Altius Space Machines, NEOs | Leave a comment

Boomerang Air-Launched TSTO RLV Concept (Part I)

Back when I left Masten to start Altius, I originally thought I was starting a launch vehicle company focused on reusable nanosat launchers. While we pivoted away from that to focus on space robotics, I’ve continued to dabble with a smallsat RLV concept that I started developing from ideas from this blog back while I was still at Masten. Since we’re definitely not in the launcher business at this point, I wanted to share the idea in the hopes that at least some of the crazy ideas get picked up by someone at some point. Without further ado, I’d like to introduce you to the Boomerang Air-Launched TSTO RLV.

What is Boomerang?
Boomerang is a concept for a low-cost, eventually fully reusable, two-stage to orbit launch system. Boomerang had the following three main system elements, which will be described in more detail in subsequent blog posts:

  • A subsonic airbreathing carrier aircraft
  • A glide-forward recovery liquid rocket powered first stage
  • A hypersonic plasmadynamic decelerator-recovered liquid rocket powered upper stage

All three components are designed to return for a precision landing at the originating air-field, with design decisions that should optimize the probability of gas and go reuse.

Boomerang CONOPS

BoomerangCONOPSWhile I will go into the CONOPS in more details in the posts about the individual system elements, the following key steps are involved in a typical mission:

  1. The two rocket stages are prepped horizontally and integrated with the planned payload to the carrier aircraft at the originating airfield.
  2. The carrier aircraft then takes off and heads up-range (ie in a direction opposite the desired launch azimuth). Once the carrier aircraft is far enough up-range for a glide-forward return, it turns around and preps for launch.
  3. The aircraft then begins to pull-up. As it nears the attitude where it can no-longer retain airspeed, the first stage begins igniting engines (what I call a “Gamma Maneuver”, although like many of my good crazy ideas, John Hare and Kirk Sorensen both beat me to the punch), enabling the aircraft to continue increasing its flight path angle to the optimal separation angle. Crossfeed from tanks on the carrier aircraft keep the first stage topped.
  4. Immediately prior to separation, the crossfeed disconnects are separated, and the rocket vehicle “drops” the aircraft of its back, and immediately begins throttling its engines up to full flight power.
  5. The first stage then performs a burn to near the optimal staging altitude and velocity. After the upper stage is released and on its way, the first stage can perform a braking burn if necessary or could potentially use a hypersonic plasmadynamic decelerator (more on that later) for some of the braking depending on what reentry speed limit minimizes the reuse complexity.
  6. The upper stage continues to orbit and delivers its payload as with a typical launch vehicle.
  7. The first stage glides forward toward the landing site. Once in the general vicinity it performs a course correction maneuver to approach the originating airfield. It then lands using either vertical or horizontal powered landing, or via an autogyrating helicopter system (still an open trade).
  8. After delivering the payload to orbit, the upper stage waits for the originating airfield to pass under its ground track again, then performs a retro-burn, and uses a hypersonic plasmadynamic decelerator to slow itself down sufficiently for safe recovery. Recovery at this point could be via mid-air recovery, horizontal powered landing, or autogyrating helicopter landing.
  9. Lather, rinse, repeat.

High Level Benefits of This Approach
While this isn’t the most orthodox approach to air launch, and does include some key, non-trivial challenge areas, it has a lot of benefits I like:

  1. The Gamma Maneuver enables launching at high subsonic speeds and flight path angles without requiring a military aircraft for launch. This can knock over 1000m/s of gravity and drag losses off of the system, which makes a huge difference for a small rocket. The gamma maneuver may also eliminate the need for large aerosurfaces or structures to accommodate large bending loads as is a traditional challenge for drop-and-light air-launched rockets.
  2. VTVL with glideforward recovery means that staging can take place at a closer to performance optimum stage velocity than is possible with boost-back or glide-back systems, since you don’t have to completely kill and then reverse first stage velocity. At worst you have to decelerate a little to make recovery easier. These two items greatly decrease the performance hit of recovering the first stage.
  3. The Gamma Maneuver with crossfeed also enables launching the rocket nearly full after having checked out all of the engines sequentially for several seconds prior to separation. Why on earth would you drop a reusable rocket before making sure its engines were all operating nominally if you could?
  4. While they’re still a low TRL technology, hypersonic plasmadynamic decelerators (HPDs, another name for MSNW’s Magnetoshell Aerocapture technology as applied to aeroentry) may greatly simplify upper stage recovery if they pan out. While they don’t give a lot of cross-range maneuverability, they do allow pretty precise up/down-range targeting, and might eliminate or at least greatly reduce the need for TPS on the upper stage.
  5. Boomerang can be initially flown with an expendable upper stage, with the HPDs added as a post-delivery experiment kit, allowing upper stage reuse to be tested-out gradually.
  6. If the stages are recovered via horizontal landing (rocket powered, mid-air recovered, or autogyro landed), that would make reintegration with the carrier airplane even easier, potentially eliminating the need for any complex restacking launch infrastructure.

Key Challenge Areas
Obviously there are some key challenges that would need to be addressed both in the design and risk reduction phases:

  1. The Gamma Maneuver scares the crap out of most pilots. I have a few suggestions for how to deal both via system design and how one could do subscale demonstrations with this that I’ll discuss in follow-on blog posts related to the carrier plane and first stage.
  2. A related issue is separation dynamics with a lit rocket vehicle. I’ll discuss this a bit in the post on the first stage.
  3. Another related issue is lighting rocket engine while attached to an aircraft, for fear of hard starts. I have some ideas for how to deal with this as well.
  4. Storing cryogenic propellants for air-launch can be a pain in the neck. I have some great ideas for this, that I’ve discussed a bit previously, and which I’ll update in one of these follow-on posts related to the first stage.

There are a lot of nuances I probably won’t be able to get into in this series, but I wanted to lay out the concept so that if someone wants to borrow/steal ideas, they can.

Next Up in Part II: Carrier Plane Considerations and Options

Posted in Commercial Space, Launch Vehicles, Orbital Access Methodologies, Rocket Design Theory | 4 Comments

Peter Jeffris

While Memorial Day is technically a day to honor those who’ve died fighting for our country, this memorial day is also almost six months to the week since Altius lost a member of its small team, Peter Jeffris, to a climbing accident on Longs Peak. Someone on NASASpaceflight.com at the time had asked if we could talk a bit about what Peter had done, and who he was. I thought it was a great idea, but at the time we were so slammed with finishing the project Peter had been working with us on that it slipped through the cracks a bit. On the drive in to work today, as I was looking up at the snowcapped mountains, thinking about how his family plans on coming out this summer to hike Longs Peak as a sort of memorial for him, I realized that now was again a good time to talk about Peter Jeffris.

Peter Jeffris

Peter Jeffris (Feb 1989 – Nov 2014)

How We Met Peter
We met Peter through Nick Correll, a CU Boulder robotics professor we had worked with on the DARPA Phoenix program a few years back. He had a Mechanical Engineering student in his robotics lab who was about to wrap up his undergraduate studies, and wanted to do something more hands-on with robotics. So Bill Bolton had him figure out how to model our 3DOF STEM Arm in ROS (Robot Operating System). The extension/retraction degree of freedom isn’t one that’s well supported by most robotics software, so it sounded like a useful project. I hadn’t been following the project very closely, since it was right when we were spooling up SBIRs and the ARM BAA effort, but Bill was following it more closely, and suggested offering Peter an internship after he graduated that summer. We couldn’t afford it, but Peter offered to work for free because of how much he loved the robotics work we were doing. After getting to see Peter in action for a few weeks, we found a way to turn his position into a paid internship position. Peter ended up being such an amazing intern, that the day before his fatal climbing accident, after our Saturday morning management meeting, our me and our finance guy were trying to figure out how we could make Peter a full-time offer to keep him as a core member of our robotics team.

What Peter Did for Altius
As an intern, Peter started work focusing on our MAGE (Mechanical Assistant for Glovebox Experiments) project, where we were trying to adapt some COTS robotics and 3d vision solutions for use inside the Microgravity Science Glovebox on the ISS, and on our 3DOF STEM Arm testbed that we wanted to use for testing various Sticky Boomâ„¢ capture mechanisms on an air-bearing table. Peter worked with the 3D vision systems and figured out how to use them to track objects and then use the data from that to allow a small COTS robot arm (lent to us by Robai) to track that object in real time. The goal was to both have a system that could allow us to track targets for Sticky Boom capture tests, as well as that would allow us to extract position data for creating bounding boxes and keep-out geometry for teleoperated glovebox experiments. Shortly before his fatal climbing accident, Peter and Bill had gone to a local elementary school to teach the kids about robotics, and show off some of the work he had done so far. They had the kids line up as robotic links to teach them how a robot arm worked, and demoed the tracking algorithm by having kids wave a blue balloon around and having the arm chase it.

Peter Jeffris working on a 3D Vision system mounted on a Robai robot arm

Peter working on a 3D Vision system mounted on a Robai robot arm

Peter and Bill teaching 2nd graders about inverse kinematics...

Peter and Bill teaching 2nd graders about inverse kinematics…

Peter demonstrating the 3D vision tracking algorithm at a local elementary school

Peter demonstrating the 3D vision tracking algorithm at a local elementary school

Peter was also helping us with our ARM BAA contract. Prior to the midterm report in October, Peter helped us put together some of the system-level CAD models for the report, such as this one:

CAD model of the Prospector/Kraken Asteroid Boulder Retrieval System for our ARM BAA interim report

CAD model of the Prospector/Kraken Asteroid Boulder Retrieval System for our ARM BAA interim report

After the interim report, when we switched gears to designing the hardware we were going to build for the final deliverable, Peter started in with sizing and sourcing the friction brakes and creating a mechanical model to support structural design of the three grasping arms. While we lost him before we could order the brakes, his design tools and brake selections ended up being what we used for sizing the final prototype hardware.

Prospector as built, leveraging a lot of the work Peter did in October and November of last year

Prospector as built, leveraging a lot of the work Peter did in October and November of last year

We were planning on also using Peter’s vision system work for mapping the boulder so the Prospector system could autonomously calculate the optimal positions for crouching the torso down onto the boulder, emplacing the jacking claws for prying the boulder off the surface, and then regrasping the boulder in free-flight post-extraction. After losing Peter, we found a group at Ball Aerospace that was working on space 3D vision systems that was willing to help us using their own IRAD funding. Though ultimately we ended up doing just a non-closed-loop scripted demo for the final demonstration in March, though we’re hoping to demo a fully closed-loop extraction at some point, as Ball and Altius IRAD priorities allow.

What Peter Was Like
Peter was one of the most impressive people I’ve had a chance to work with during my career in aerospace, even though he was only 25 at the time of his accident. I can’t do justice to him in a short description, but some of his best attributes were:

  • Fearlessness: Both in the outdoors but also in engineering, Peter pretty much never showed fear. During a memorial his family did the week after his death, they showed a slideshow of pictures, including one of his favorite hangouts in a hammock up at the top of the Flatirons near Boulder. Me, I’m terrified of heights–Peter seemed perfectly at ease. In engineering, if Peter didn’t understand something, he’d just jump in and learn it. No problem we threw at him was something he was worried he couldn’t figure out.
  • Dedication/Stubbornness: When Peter jumped into a new problem, he wasn’t going to let obstacles stand in his way. If someone’s code wasn’t doing what he wanted to do, he’d write his own, even if it meant burning the midnight oil multiple nights. Once he set his mind to a task, he’d absolutely refuse to stop until he had beaten it into submission.
  • Fun Loving: Peter always had a goofy half-grin on his face when he was doing something he enjoyed. He had a sort of optimistic and adventurous spirit that pretty much everyone I knew who knew him loved.
  • Helping Others: Peter was an Eagle Scout. He built homes for Habitat for Humanity. And he put in countless overtime hours preparing to teach and inspire a classroom of 2nd graders about robotics.

He was a talented programmer, a good budding robotics controls guy, rock solid at mechanical engineering and kinematics, and just the kind of guy that everyone loved working with. It was heartbraking losing him, and we had only known him for a few months.

The Accident
For those of you who didn’t follow my previous notes about what happened, here’s the basic rundown of events leading up to Peter’s death on Longs Peak. It’s been six months, so I’m probably forgetting important details, but this gives a high level review of the tragic events.

  1. Peter had a group of hiking buddies he’d go climbing with while at CU Boulder. He had scaled Longs Peak (one of the deadliest 14ers in Colorado) several times with them, including one time he had solo’d and snow boarded down afterwards.
  2. He had tried to get a group together to scale Longs Peak that weekend, but most of his team had scattered after graduation from CU a few months earlier. When none of them could make it, he decided to climb the mountain by himself (as he had at least once before).
  3. That week ended up being one of the first major snowstorms of the winter. In spite of the crappy weather, he had set the goal to make it, so he didn’t turn back. He packed light intending to do a rapid summit and return. He was skilled at winter survival including snow caving and such, but decided to pack light in the hopes of being able to move quickly.
  4. The camera they found on him has a selfie video he took from the summit around 4:30pm the day he died. Normally for Longs Peak, people will camp out and start hiking around 5am so they can summit by noon and be back off the mountain by dark. Peter had persevered and reached the summit only shortly before nightfall. The winds were heavy and all around the summit you could see the snowclouds plowing through.
  5. On the way back down, about a 1/4 mile from the “Keyhole” Peter got off the trail, whether accidentally or intentionally, and was climbing above the normal trail across the “Narrows” (a narrow ledge leading about half a mile above sheer drop-offs), when he fell. The fall was over 600 feet and was probably instantly fatal.
  6. He had told some of his coworkers that he was going to climb Longs Peak on Sunday, and when he didn’t show up for work on Monday, we got worried. One of the other engineers had the wisdom to call the park rangers to check the trailhead, where they found his jeep.
  7. The weather for the next three days on the mountain was so bad that they couldn’t get search and rescue people above the timberline. Winds were gusting at well above 80 miles per hour with temperatures well below freezing. When the weather finally let up four days later, they were able to find Peter and recover his body.

I’m sorry if that description is a little antiseptic. That was one of the roughest weeks of my adult lifetime, hoping and praying that they’d find him, and eventually just praying that they’d be able to find his body so his family would have closure. I’m grateful for the search and rescue folks who risked their life to find him and return him home, even after it was clear that he hadn’t made it.

It’s always sad losing someone young like that. It’s even harder knowing that he was less than 1/4 mile from a place he could’ve holed up for the night and made it home safely. As his parent said though, he died doing what he loved, and while he made some poor decisions leading up to his fatal accident, they were mostly driven by the attributes that made Peter the wonderful person that he was.

Peter wasn’t a particularly religious person, but he was a good person. While I know that many who read this blog find religion and faith to be a bunch of irrational poppycock, I know for myself that I’ll see him again, and I look forward to that day, and I look forward to seeing him reunited with his family that loves him so much. It doesn’t take away all or even most of the pain of losing a friend, even one that I had only known briefly, but I do have a testimony of the eternal nature of the human spirit, and that the day will come when all will live again. That day when sorrows are forgot and loves purest joys are restored is one that is beginning to mean a whole lot more to me the longer I live, and the more absent friends and family I have waiting for me beyond the veil.

And that same sociality which exists among us here will exist among us there, only it will be coupled with eternal glory, which glory we do not now enjoy. (D&C 130:2)

Posted in Altius Space Machines, Friends | 2 Comments

My Mom’s Homeschool Training Site: Mentoring Our Own

I was talking with my parents tonight and realized that a good topic for a Sunday post would be to introduce my mom’s company’s new website: Mentoring Our Own. My mom’s company is about teaching and mentoring new homeschooling parents, and helping them learn how to teach their children at home. She’s been running this and other related home-education businesses for the past decade and a half.

My brother-in-law (who is a great graphics artist) made my mom this avatar for her website:Mentoring-Our-Own-donna-goff_icon_illustrated-iconIf you’re interested in homeschooling, but not sure where to start, you might want to check out her website and blog.

Posted in Family, Homeschooling | 1 Comment

More EGT Musings: ISRU Propellants

One of the ideas I had been thinking of blogging about was the thought of augmenting EGT asteroid deflection with in-situ derived propellants. The gravitation attraction force is usually the bottleneck in how fast you can do an asteroid deflection, but in some situations the propellant load might matter too.

What options are there for ISRU propellants in this case?

  • If the asteroid is a carbonaceous chondrite, water might be your best bet. There are some promising SEP technologies, like the ELF thrusters being developed by MSNW that can operate efficiently with water as the propellant. The challenge is that water is only present in some asteroids, might not be super easy to extract, and might require enough infrastructure to not be worth it on net.
  • The other big option is asteroid regolith. This could be charged up and run in a similar manner to an electrospray engine, or if it the dust is magnetically susceptible, it could be accelerated by something similar to a coil gun, mass driver, or linear accelerator. One of my employees used to work at a LASP lab running a dusty plasma accelerator. Basically they’d charge up small particles of dust, put them in a crazy electric field, and accelerate them to ~100km/s to smash into other dust particles to study micrometeorite formation processes.

What are some of the considerations for such an idea?

  • You are probably going to be very power limited. This both impacts what you can do as far as propellant extraction, and also limits the exhaust velocity/Isp that is optimal for an asteroidal ISRU-fed propulsion system. Just as ion engine systems operating in gravity wells typically tend to optimize to a lower Isp/higher thrust, the optimal deflection per unit time likely won’t come from the highest theoretical Isp.
  • On the other hand, the lower the exhaust velocity, the more material you have to handle to produce the “propellant”. So the optimal exhaust velocity is likely somewhere in the middle.
  • Also, if you’re extracting water, that’s likely more energy intensive than dust.

Without running the detailed numbers, my guess is you’d want a dust “electrospray” engine with an Isp in the 100-1000s range to optimize the balance between thrust per unit power and required extraction capabilities. For instance a 500s Isp is maybe 25% of the Isp of the Xenon Hall Effect Thrusters they’re thinking of using for ARM. That would imply getting somewhere between 16x the thrust per unit time as running the same amount of power through the HET.You’d need 16x the propellant mass flow rate, but if you’re gathering hundreds of tonnes of regolith, rock, and boulders, I would think that wouldn’t be that hard to get say ~125tonnes of regolith. One nice thing is that some of this material can be gathered while landing to gather the additional mass for the enhanced gravity tractor.

Food for thought?

Posted in NEOs | 2 Comments

Random ULA Thoughts

[Disclaimer: My current company and former company have both done work with ULA. In fact, we just started another small IRAD project with ULA. We’ve also done work with SpaceX in the past, but our current work with ULA is a potential bias I wanted to state up front. I’m not being paid by ULA or encouraged to make these points, and I don’t have any super-secret inside knowledge about Vulcan or their inner workings. This is just my opinion, and I feel like I need to share it, even if people will blow me off as being a ULA shill.]

There is a lot of debate swirling around the future of ULA, Vulcan, the RD-180, etc. I had a few quick thoughts I wanted to share that I think don’t get a lot of air-time. While these could be construed as pro-ULA, I’m also on the record as being a fan of real competition, letting SpaceX compete for DoD contracts as soon as possible, and getting rid of the ELC subsidy for ULA. Here’s my thoughts:

  1. While creating incentives to wean ULA off of the RD-180 may make some sense, there is no good reason for doing so in a way that hobbles ULA and makes it impossible for it to compete with SpaceX.
  2. Some will point out that Russia threatened to cut off supply of the RD-180, but the reality is they have no good reason to do so, and really hold very little leverage over the US once SpaceX is certified to fly EELV-class national security payloads. Cutting off the RD-180 only strengthens SpaceX, the one serious competitor to the Russian Soyuz, Proton, and Angara vehicles. No, the RD-180 “supply issues” are entirely a creation of our Congress.
  3. We bought titanium from the USSR during the Cold War, and as mentioned above, Russia has even less leverage on us today with RD-180s and Atlas V than it did then with Titanium supplies.
  4. ULA really does need to downselect to just one launcher family to be competitive. And the only reason it didn’t do so sooner was because without SpaceX being certified for DoD payloads, the DoD required them to keep both EELV families flying for assured access purposes. By ditching over half of their pads, over half of their configurations, etc., they can significantly consolidate their supplier base, and cut down on duplicative capabilities. They would’ve already done this if the DoD had allowed them to previously.
  5. The move to drop Delta-IV is not just a cynical move to try and force our Congress to not be stupid re: the RD-180. And it’s not just that the Delta-IV is less competitive (but you’d think that letting companies shed uncompetitive product lines wouldn’t be such a sore spot with so-called commercial space enthusiasts…). Vulcan is based on the Atlas V and Centaur. If Atlas V were retired, it would be nearly impossible to keep the Atlas V/Centaur supplier base alive long enough to get Vulcan flying. Could you force Vulcan to be more Delta-IV derived so you could force them to shut down their more competitive launcher? Sure. It would just guarantee that Vulcan wouldn’t be as competitive in the marketplace, wouldn’t be as capable, and would be less useful to our military. Could you do it anyway? Sure. And you could stick your hand in the blender and turn it on. There’s no limit to stupid self-defeating things you could do if you put your mind to it. Does anyone else see how ridiculous this line of thinking is though?
  6. The US is served far better by having two healthy and competitive launch service providers than it is with either a ULA or a SpaceX monopoly. It’s also much better served by a healthy SpaceX and ULA w/ Vulcan than it would be with a healthy SpaceX and a ULA that’s only kept alive on life-support from the government. Just as we were all better off with Intel and AMD, Windows and Mac, Apple and Samsung, we’re better off having healthy competition than artificially stifling things in either player’s favor.

I don’t think it’s the government’s job to make ULA successful, but they shouldn’t be telling them what launchers they can build and what engines they can buy either. Make them compete, but let them compete!

Posted in Space Policy, ULA | 33 Comments

Minor Blog Upgrades

This is sort of a cheat for meeting my blog-a-day quota for this last month, but I wanted to note a few minor tweaks I’ve made to the blog. I’m not really savvy with all the coding experience needed to modify javascript, .php, or CSS stylesheets, so they are pretty simple tweaks, but hopefully they’ll improve people’s blog reading experience.

Specific changes:

  • I’ve enabled the use of comment and author avatars. I wanted a way of helping people tell which posts were mine and which were those of the other bloggers, as there’s been occasional confusion. I wasn’t able to figure out how to splice in the code to display our avatars next to each post title, but it’s a start.
  • I added a bio block at the bottom of each post (when you click on the individual post), serving the above mentioned function of making it clear which of us wrote which post.
  • I added a profile picture/avatar that’s recent enough to show me with my beard (and all the grey hair I’ve earned between two space startups and four little boys).
  • I also installed a plugin that lets me add footnotes to my blog posts.1
    • The footnotes appear if you mouseover the footnote number, or you can see them in the footer if you go to the specific post. I can’t figure out how to show them above the author bio, but really, I mostly just wanted them as mouseover text.
    • Hopefully this should enable a slight decrease in my abuse of parenthetical and nested parenthetical statements, and slightly increase my use of witty sarcasm.
  • I still need to find a header picture that works and doesn’t suck, so the default one will stay for a bit longer.

Tomorrow I’ll blog something with real content.

Posted in Administrivia | 1 Comment

Additional EGT Musings: Gravity Tractor and Enhanced Gravity Tractor Overview

[Editor’s Note: When I posted the Enhanced Gravity Tractor article earlier in the week, I didn’t have time to really dig into the concept the way I had originally intended. Josh Hopkins suggested on Twitter that I could cheat and revisit the topic in a follow-on blog post since I’m trying to do this blog-a-day for this last month leading up to the 10th anniversary of Selenian Boondocks. This is probably the first of two or three follow-on posts]

The previously linked-to EGT paper had a great introduction to the concept of using a gravity tractor for deflecting potentially hazardous asteroids. In all gravity tractor concepts you’re using the mutual gravitational attraction between the spacecraft and the asteroid itself as a way of transferring thrust from the spacecraft’s thrusters into the asteroid itself. You can do this using an in-line tractor orientation, where you cant the spacecraft engines outwards at an angle sufficient to avoid plume impingement on the asteroid, and you eat the cosine losses on the thrusters.

In-lineTractoringOr you can place the spacecraft into a halo orbit around the asteroid, and fire the thrusters due backwards.This shifts the orbit from orbiting around the equator of the asteroid to an offset halo (that looks like a spiral from a sun-centered perspective).

Spiral TractoringI prefer the halo approach, both because you can probably make it passively safe (where a thruster failure doesn’t involve the spacecraft colliding with the asteroid), because you can probably have your spacecraft a lot closer to the asteroid thus increasing the gravitational acceleration (and thus peak thrust you can impart), because you avoid the cosine losses from canted thrusters, and because it’s a lot easier to add multiple gravity tractors flying in formation with the halo/spiral approach.The equation governing the thrust you can impart into an asteroid in such a halo orbit is:Haloing EquationWhere rho is the radius of the halo orbit, and z is the axial offset distance of the halo orbit, G is the universal gravitational constant, Mast is the mass of the asteroid, and Msc is the mass of the spacecraft. As you can see, the closer you are in, and the heavier your spacecraft, the more force you can transmit into the asteroid, hence the idea of augmenting the spacecraft mass with locally harvested regolith, rock, and boulder materials. It is pretty easy to increase the effective towing mass by >10x using locally harvested materials. While traditional gravity tractor methods required more than a decade of advanced notice, enhanced gravity tractoring might only take a year or two of advanced notice if you already have the infrastructure in place to deal with a threat.

As an interesting aside, I noticed the other night that it looks like my coblogger John Hare might have actually beat the NASA guys to coming to this conclusion by at least a few months, based on this Selenian Boondocks blog post from February 2013, which describes a concept almost identical to the one shown in Figure 20 from the paper.

Posted in NEOs | 13 Comments

Random Thoughts: Fasting With a (Secular) Purpose

As a practicing Mormon, one part of our religious practice is a monthly fast. But I’ve been finding that many people also do fasting for non-religious dietary or health reasons. This short blog post is directed at people fasting for these non-religious reasons, as a possible way of making your experience more meaningful by borrowing a secularized page from those who fast religiously.

Specifically, an element of an LDS member’s fast is to take the money that you would’ve spent on food and donate it for helping the poor and the hungry. We do this through what are called “fast offerings” which a local congregation’s bishop uses to provide food and help to the less fortunate in the congregation, often through a “bishop’s storehouse.” But the general concept of taking the money you save by not eating and using it to donate to what you see as a worthy cause is what I want to focus on.

For instance, you could donate the money you save to:

  • As food or money to a local food kitchen, a shelter for troubled youth, or something similar focused on alleviating local poverty.
  • A good non-poverty related cause, like privately-funded space telescopes for detecting hazardous asteroids, promoting criminal justice reform, environmental research, education, robotics classes for kids, or any of a host of other good causes.
  • Helping someone specifically, like maybe buying some seeds and gardening materials to help plant some flowers for an elderly neighbor, or buying parts or tools to help a friend or neighbor repair a car or a bike, etc.

The point is, use the money you would’ve spent anyway on food to do something special for someone else. I think you’ll find it easier to stick with your fast when you know the money you’re saving is going to help a cause or person you care about, and it will likely make your fasting more meaningful. At least that has been my experience. When my religious fasting slips into “checking off a monthly to-do,” it’s a chore that I look forward to ending. But when you’re really doing it to help someone else, it really does feel a lot easier.

In religious lingo we’d call this “fasting with a purpose”, but the idea is perfectly at home in a secular context as well.

Posted in Random Thoughts | 2 Comments

Enhanced Gravity Tractor Paper at the IAA Planetary Defense Conference

I’ve noticed that very few people seem to understand the concept of the Enhanced Gravity Tractor planetary defense technique that the ARM Option B approach plans on demonstrating. A friend recently forwarded me a great paper describing this concept that was presented last month in Italy at the IAA Planetary Defense Conference, that provides a good introduction to the concept:

IAA-PDC-15-04-11 Enhanced Gravity Tractor Technique for Planetary Defense

The high level version is that by collecting mass from the target asteroid, you can enhance the diversion speed of an asteroid by 10-50x or more compared to using a normal gravity tractor without local mass augmentation. This means that even for an Asteroid Redirect Vehicle with a capture mechanism about the size Altius analyzed in its ARM BAA study, you could redirect an earth-crossing 100m class asteroid with <1yr notice, and a 150m diameter (Tunguska-class) asteroid with <2yrs.

There were a bunch of points made in the paper, but a few of the more interesting ones are:

  1. Because an enhanced gravity tractor works via gravity, you could use it to divert debris from an unsuccessful nuclear diversion attempt.
  2. You can speed up the process by putting multiple EGT spacecraft into a halo orbit around the asteroid simultaneously.
  3. The EGT doesn’t necessarily require boulders on the target asteroid. If the redirect spacecraft has the ability to scoop regolith for instance, you could use regolith or smaller rocks instead of a boulder extractor system.

There’s a lot more to it than that, but I wanted to put this article up there because I think most people following ARM, especially critics, could benefit from access to the article.

 

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