I didn’t have a chance to watch either of the House subcommittee hearings today, so I’m grateful that Clark linked to the testimonies of the various witnesses. I really enjoyed reading Brett’s testimony, and thought one of his points in particular is worth repeating.
To me one of the more interesting points is found at the top of page 11. There were several misleading statements made by several people today about the relative safety of Ares-I compared to commercial crew vehicles. As Brett put it (my emphasis added):
Second, some have claimed that NASA’s Exploration Systems Architecture Study (ESAS) shows that the current exploration vehicles are safer than commercial crew vehicles. In actuality, commercial crew vehicles were never even analyzed in the ESAS report – the ESAS report only looked at vehicles large enough to carry Orion, such as Ares I and variants of the triple-core Delta IV Heavy, and did not examine the smaller, simple, single-core vehicles, such as Atlas V Medium and Falcon 9 Medium that are sufficiently sized for commercial crew missions. Moreover, even if ESAS had compared exploration vehicles to commercial crew-sized vehicles, the comparisons would be “apples vs. oranges,†because of the dramatically different tasks of these two types of vehicles.
When Jeff Hanley talks about how the Great Oz and supercomputers at NASA show that Ares-I is 3x safer than commercial launch vehicles, I wonder if he’s ever going to release their analyses for actually commercial crew vehicles, or if he’s being accidentally or intentionally dishonest. Because so far we haven’t been shown any data about the safety of actual commercial crew launchers. So far we have lots of data shown for the risks of using existing or modified commercial launch vehicles for launching a massive spacecraft designed to go to and return from the moon, including significant plane change maneuvers to allow anytime returns (ie Orion). It’s interesting to note that over half of the mass on Orion is the oversized launch escape system needed to get away from an SRB you can’t shutoff, and enough propellant for about 1500m/s of maneuvering to reach orbit and then to do in-space ops. That’s above and beyond the RCS propellant on the CM itself.
Most of the stuff that make Orion so massive are flat-out completely unnecessary for an earth-to-LEO crew capsule. You don’t need those kinds of delta-V capabilities. You don’t need as roomy of facilities, since by definition the flight times should be a lot shorter. Etc. There’s a reason why almost all of the proposed commercial crew systems are able to utilize single-stick launchers like Atlas V or Falcon 9–for an actual earth-to-LEO capsule you really don’t need anything bigger.
This realization that earth to LEO capsules can be much smaller than Orion leads to at least two important corollaries that I can think of:
- Smaller capsules mean higher structural margins. One of the existing vehicles most often suggested for commercial crew, Atlas V, was designed for the worst-case loading environment of any of its configurations (in this case I believe that would be the Atlas V 551 or 552). The Atlas V 552 sees much higher max-Q’s than the 401/402 do, and has a much heavier payload on top, which exerts much larger structural loads on the Centaur stage than are seen in the 401/402 configuration. While the Centaur structures may not meet the 1.4 magic number NASA likes in some of the bigger configurations, as I understand it, it actually exceeds that number in the 401/402 config most likely used for commercial applications. The Falcon 9 was designed from the start to meet NASA structural margin specs.
- No need for strapons. Only one of the commercial crew ideas I’ve seen so far used a vehicle with strapons for crew launch (Dreamchaser). This alone should make a huge difference in launcher reliability, since there are less things that can go wrong, less staging events, etc. Most of the commercial launcher ideas they mentioned in ESAS assumed multi-core configurations.
There’s also the possiblity on the Atlas-V of using a dual-engine Centaur configuration to allow for some upper stage engine-out capability, or running the RL-10 at a derated performance level (not sure if that’s something it can do automatically, or if you’d have to make modifications–if you have to modify it it probably isn’t worth it). With the much lower max-Q, and the ability to shut off the booster engine in case of an abort, I have a hard time believing that Ares-I is really that much more reliable than an actual commercial crew capsule launched on a commercial launch vehicle that has dozens of flights under its belt.
Food for thought.
Jonathan Goff
Latest posts by Jonathan Goff (see all)
- NASA’s Selection of the Blue Moon Lander for Artemis V - May 25, 2023
- Fill ‘er Up: New AIAA Aerospace America Article on Propellant Depots - September 2, 2022
- Independent Perspectives on Cislunar Depotization - August 26, 2022
>> or running the RL-10 at a derated performance level (not sure if that’s something it can do automatically,<<<
Didn't they run the RL-10s on the DC-X at under 50% power?
just glancing at wikipedia they list the GLOW for DC-X at 18,900 kg and dry weight at 9,100 kg, adn the RL-10s thrust at 6,100 kgf each. The NASA site says the RL-10s are throttleable from 30% to lOO%.
To my shame, I have drifted away from this beautiful site again. Googling around, it appears that Atlas V 402 can lift something like 12.5 metric tons to LEO (with 4 meter fairing). What sort of vehicle (including escape system) can be crammed into that much space?
Karl,
No worries about drifting from the site a bit. I’ve been pretty lousy at keeping it updated on a regular basis this last year. Between Peter Yuri showing up this April, the LLC stuff, writing and help writing white papers for the A-com stuff, and my first ever conference paper, something had to give. I’m likely going to be tied up in a few papers this next year (a tuggery one, possibly one relating to depots, and possible one relating to a new rocket engine cycle that’s really intriguing), but work shouldn’t be as brutally hectic, and I’m getting used to having three little balls of entropy running around….sooo…I should hopefully be doing stuff to earn back some of my longtime readers.
As to your comment about the 402. You can take two approaches. One is to make a bigger crew module (though you can already fly 4-8 people in the 20klb that the 401 can deliver to LEO), the other approach is to keep the module smaller, leave some spare capacity, but give you more engine-out capability, and abort options. If you were going to a station collocated with a depot, the excess propellant you didn’t use by such a maneuver (about 2 mT of it per flight) could be sold to the depot after the fact.
Food for thought.
~jon
For bigger payloads, the Delta IV heavy without an upperstage is a fancy that was looked at. There should be a lot of structural margin there! Though it is a big change in configuration. 🙂
I couldn’t agree more that some single-Core LVs are much better choices than Ares-I. Notwithstanding the fact that it’s not single-core, do you know what kinds of strap-ons are envisioned for Dream Chaser? I’m a little skeptical that a dual-engine Centaur would have much engine-capability. Surely loosing half of the propulsion would entail a very large performance hit, so payload margins would have to be kept very large to provide for tolerance of an engine failure for a significant portion of the stage’s burn time.
Nels,
If you think about it, a DEC is an SEC with a slightly different thrust structure, some extra plumbing, and another RL10. I’m not sure what the weight delta is, but it’s something like 500lb. If you had a payload that weighed 500lb less than the carrying capacity of a 401 (or maybe add a little margin on top of that), then even if one of the engines didn’t light right at the start, you’d still be able to make orbit, wouldn’t you?
~Jon
You’re right. I was applying unmanned logic to a manned vehicle. If there are people aboard, then there’s a large safety advantage to being able to reach some kind of orbit, even if it’s much lower than the intended one. I guess the other question that comes to mind is whether it’s feasible to gimbal the good engine far enough to maintain stability (a Centaur engine failure in 1991 resulted in a tumble).
Nels,
Now the gimballing question is a better one. At engine start I don’t know where the CG is. Not sure what the gimbal range on the RL-10 is either. It might be a case where it only offers engine-out for part of the burn duration. Don’t know. May have to ping my ULA friends.
~Jon
I would imagine you could make the RL-10 gimbal range whatever you wanted within geometrical constraints of the vehicle. It’s not an intrinsic feature of the engine.
And at ignition gimbal each engine so it acts through the center of mass, just in case the other engine doesn’t ignite or suffers transients.
Part One:
Something like an AtlasV 401/402 adaptation could be very close to being a perfect launcher for a spacecraft similar, in overall assumptions, to something like the Russian Soyuz or the Chinese Chenzhou. By this (the similarity comment) I’m not necessarily making reference to the three-module design approach of those spacecraft but, instead, making a generic reference to main spacecraft diameters (vs main launch vehicle diameters), total spacecraft mass (~8t) vs spacecraft dV budget (~300 m/s should be more than enough for LEO… beyond LEO capabilities could be achieved with proper space stages/tugs interactions) and other capabilities, abort options, launch vehicle integration, etc.
As a side note, just for fun, ‘played’ a few months ago with the concept on my 3D / simulation archives (one example: integrating something similar to Soyuz on top of the simplest Atlas V configuration… nice performance and also, why not say it too, a very good looking launcher-spacecraft configuration!; think that might still have some images / simulation files about that somewhere).
Please note that I’m not defending the idea of placing a Soyuz or Shenzhou on top of an AtlasV, only trying to write that something like an AtlasV 401 / 402 could then be a good match for a new conceptual crewed spacecraft where such spacecraft could have a maximum diameter smaller than ~3m (or else, not much beyond the ~4m) and a command module capsule capable of carrying at least 3 astronauts (or more, depending of specific spacecraft design assumptions), all this while having a ‘standard’ abort system (by this I mean something very similar to the current Soyuz / Shenzhou abort systems) and also while presenting a +/- clean and smooth overall outer mold line for a +/- standard AtlasV 401/402.
Part Two:
Having written the above, another different approach would be to go for a larger diameter capsule (larger than Centaur upper stage and/or even than the first stage diameter) and also for a heavier (~7t or more) capsule, with a minimal service module… Something like what seems to be the idea behind the ~5m diameter Orion-based outer mold line capsule of ‘Orion-Lite’ spacecraft concept.
However, on such case, I was not able to fully research and/or understand yet some of the integration, performance, abort constraints and mission design impacts that such kind of crewed spacecraft vehicle vs AtlasV integration could mean…
… A few examples of open questions (not much public info available) for such kind of larger capsule / spacecraft AtlasV integration: abort system design parameters (and capabilities, eventual hybrid abort/insertion role?), would an AtlasV 402 actually become an AtlasV 502 (with Centaur fully enclosed) for such kind of spacecraft type integration (due to structural loads and other integration aspects), etc, etc. Related with this, please note some of the questions that tried to ask at:
http://forum.nasaspaceflight.com/index.php?topic=6479.270
Summary / Conclusion and Extra Food for Thought:
In any of the above cases the assumptions for the crewed spacecraft and for the launch vehicle integration (in this case, the simplest possible AtlasV) are just some of the things that would need to be better studied (together with proper trajectory tweaking, ascent simulation and overall mission design) in order to actually put some numbers into the talk, at least to have a better (or more specific) starting point for the discussion and a better idea of what the simpler no-solids EELV variants (in this case, AtlasV) can actually provide in terms of safety, performance, mission design and mission capabilities for crewed roles (vs specific spacecraft and mission design assumptions). The other side of the coin is that doing these kind of more elaborated ‘studies’ takes a bit of time (and, as noted above, there is a little of public information missing for some specific brainstorms, related with more specific spacecraft possibilities).
António
PS1: Jon, as you might remember, wrote some musings about these kind of AtlasV 401/402/502 vs commercial crewed spacecraft brainstorms over at NSF forums, also produced a couple of images about that on my flickr site (by the way, if wanting, feel free to use / link any of the images in your articles or ask for specific imagery: if having time or if having something ready I will gladly try to provide stuff from the archives here 😉 )
PS2: Only for completeness, will take the liberty of linking to the thread on NSF where made a number of conceptual brainstorms about Orion-Lite (maybe one day will return to those brainstorms, if meanwhile find some LV/spacecraft missing info that would need for better simulation work) :
http://forum.nasaspaceflight.com/index.php?topic=18323.0
What I took away from this pep rally was that once again NASA representatives have said, on the record, that they can’t see any other customers for commercial crew-to-orbit services. The claim was made thee separate times and now has been backed up by a COTS contract recipient. This is blatantly, and obviously, false.
I have personally spoken with the vice-chairman of the board of directors for Space Adventures and he tells me that they are ready and willing to buy seats from SpaceX or any other company. They don’t even need to fly to the ISS, there are customers who would happily stay in the capsule for the duration of the flight.
Both Jeff Foust and Brett Alexander were at the table when we had this discussion. Someone needs to call these NASA representatives on their bullshit, in public and on the record, before their version of reality becomes accepted fact.
SpaceX did not sign many launch contracts with civilian companies until it had successfully launched the Falcon 1. Now Bigelow and ORBCOMM are customers.
The same believe it when you see it is likely to happen with manned space flight.