Ares-I Ascent Reliability: Still Missing The Point

I listened in a bit on yesterday’s Augustine Committee discussion.  The debate at the end between Bo and the others reminded me of a point I’ve made a bunch of times on this blog–that when you’re talking about exploration missions, ascent reliability is only a small component of the overall risk.

Since I’ve been doing a lot of rocket plumbing, let me use an analogy.  Imagine you have a small rocket engine, like our igniter.  It’s got a tiny fuel orifice that’s only a tiny fraction of an inch in diameter.   Now, if the solenoid valve upstream of that orifice is small enough, it can meaningfully decrease the overall flow.  But after you reach a certain valve size, the valve size ceases to be relevant to the overall flow rate.  You could put a 1″ full port ball valve leading up to that orifice, and the flow difference between that an a solenoid valve with a 1/32″ port is going to be round-off error.  Once the size difference between the most constricting component and the rest of the components gets past a certain point, you can pretty much ignore them.

There are tons of other analogies from electronics, manufacturing, structures, etc.  Basically, in almost any system, you can improve one component only so far before you hit rapidly diminishing returns.  A wise engineer will spend his resources in a way to maximize the overall system reliability, not just one small sub-component.

Unfortunately, that’s exactly the mistake that the CxP guys have been making with Ares-I.  Even if, in spite of all evidence so far, and in spite of all historical precedent, Ares-I really is as reliable as their Probibalistic Risk Assesments suggest, it still isn’t a wise investment of capital when you look at the overall exploration mission.

Let’s just go back to the math again.

According to ESAS, the predicted probability of losing a crew on a lunar mission was something like 1.6% (or about 1/60).  Of that, only about 1/2000 (or .05%) came from ascent risk–or about 3% of the overall crew risk for the entire mission.  A mission that used the worst numbers they came up with for existing EELVs with an LAS attached estimated a 1/600 probability of losing a crew (or about .16% chance).  That would increase the probability of losing a crew to 1.7% or about 1/59…

Investing tens of billions of dollars to reduce the probability of losing a crew from 1.7% to 1.6% only makes sense if there are no better safety investments out there.  With a 1/600 ascent safety rating, about 90% of the danger to the crew is coming from other phases of the mission–which strongly suggests that the best safety return on investment is not in overoptimizing the ascent reliability.

Now, to be fair, Shuttle has a safety rating estimated to be around 1/100.  At that reliability rating for crew launch, it would be one of the dominant crew safety risks in a lunar mission.  Spending money to get it up past the 1/500 range is a good investment.  But after a point, if your goal is to improve the overall probability of getting a crew safely to the moon and back, you’re best off finding other areas to invest your money.

On a related note, the self-righteous attitude that many CxP people like Griffin and Hanley take that the Augustine Committee is ignoring crew safety is kind of farsically hypocritical at best.  Blowing so much of your budget on ascent risks, when they aren’t the dominant risk is actually making the overall mission less safe, not more.  Wisely spending that money instead on mitigating the risks in lunar landing, ascent, surface ops, and earth return would result in a higher probability of not killing astronauts on a given mission.  If astronaut safety is really so important to CxP, why do they only seem to care about the first 5-10 minutes of the mission, when it’s the rest of the mission that accounts for 90-97% of the danger?

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Jonathan Goff

Jonathan Goff

President/CEO at Altius Space Machines
Jonathan Goff is a space technologist, inventor, and serial space entrepreneur who created the Selenian Boondocks blog. Jon was a co-founder of Masten Space Systems, and is the founder and CEO of Altius Space Machines, a space robotics startup in Broomfield, CO. His family includes his wife, Tiffany, and five boys: Jarom (deceased), Jonathan, James, Peter, and Andrew. Jon has a BS in Manufacturing Engineering (1999) and an MS in Mechanical Engineering (2007) from Brigham Young University, and served an LDS proselytizing mission in Olongapo, Philippines from 2000-2002.
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23 Responses to Ares-I Ascent Reliability: Still Missing The Point

  1. Martijn Meijering says:

    If astronaut safety is really so important to CxP, why do they only seem to care about the first 5-10 minutes of the mission, when it’s the rest of the mission that accounts for 90-97% of the danger?

    That’s a rhetorical question, right? It’s about where the money goes, who is in control and who gets to look good. Sadly, the space program only exists to buy votes.

  2. john hare says:

    I find it quite annoying when conspiricy starts sounding like a rational explanation.

  3. one says:

    the simpler design should make the Ares-1 up to three times more reliable than a Shuttle-C/Ares-5-lite and up to five times safer than a Falcon-9 but, unfortunately, the Ares-1 can’t fly and is also a dangerous rocket due to several reasons

  4. Gaetano,
    Which is it? Is the design actually simpler and more reliable than those others, or is it “a dangerous rocket due to several reasons”. It can’t be both. Unless you’re saying that “in theory it should be safer, but in practice it probably won’t be”. In which case I actually agree with you.


  5. one says:

    “in theory it should be safer, but in practice it probably won’t be”

  6. Pete says:

    If astronaut safety is really so important to CxP, why do they only seem to care about the first 5-10 minutes of the mission, when it’s the rest of the mission that accounts for 90-97% of the danger?

    That one is easy – the first 5-10 minutes is the most visible. It is not actual safety but the public perception of safety that matters to NASA. 🙁

    The other safety hypocrisy that greatly bothers me is that one can probably not achieve and definitely not demonstrate high safety levels at low flight rates. By going out of their way to select low flight rate vehicles NASA is demonstrating that they do not take safety seriously.

    More cynically, very long development times and low flight rates enable NASA to pretend to very high safety levels for a very long time before any evidence to the contrary can present itself. By which time the world has forgotten and moved on.

    It particularly bothers me that NASA dismisses the safety of New Space where high flight rate solutions are being developed. Sure the safety of new low cost high flight rate solutions may be lower in the short term, but in the long term they will be much higher. In real terms, New Space is taking safety far more seriously than NASA, by bravely adopting a new architecture that can evolve to much high safety levels. NASA’s current holier than thou argument on safety is indefensible.

    NASA’s safety culture has little to do with safety and everything to do with short term political expediency – the perception of safety, and with it their next funding round. How many more people will they kill for their jobs program?

  7. A_M_Swallow says:

    Safety considerations have to consider function. The calculations appear to be based on a methodology for predicting the number of spare parts needed. Removing the brakes from a car will reduce the number of parts but will increase the number of breaks.

  8. Pete,
    That one is easy – the first 5-10 minutes is the most visible. It is not actual safety but the public perception of safety that matters to NASA. 🙁

    My question is, is a fatality in the first 5-10minutes really 30x worse PR-wise than fatalities at any other time? Is a quick death that NASA can spin as “instantaneous and relatively painless” going to be 30x more acceptable to the public than finding out that the astronauts asphyxiated themselves around the moon due to a botched earth return burn, or had their lunar lander lithobrake, or any of a number of more likely failure modes? I’d be willing to believe that getting the failure at least out where it can’t be easily seen may be somewhat better from a PR standpoint, but 30x better? I doubt it.

    That said, I agree wholeheartedly with the rest of your comments.


  9. Anonymous says:


    Excellent post again!!

    Using the logic within this post, are all of the manned Mars mission archtectures crazy in terms of crew safety for selecting chemical propulsion options that lead to 2 to 3 year missions instead of investing in near-term nuclear-electric propulsion (or other) options that could reduce mission time to under 6 months. I am assuming that shorter missions under 6 months are safer than longer 3 year missions to Mars, and that suitable Nuclear-Electric (or other) high delta-V options could be developed easily within 10 years if NASA diverted $10 Billion from ARES-I to practical “new propulsion” developments.

    If this were a 2 or 3 year human mission to Mars using the ESAS LEO rendezvous architecture instead of a 2 to 3 week mission to the Moon, then how would your analysis change? NASA’s current DRM 5.0 strategy for a manned Mars mission involves 1 Ares-I launch and 2 Ares-V launches to assemble the vehicle that will take the Astronauts to Mars, and there are 4 others Ares-V launches required to assemble and send the other 2 vehicles to Mars for the full mission.

    I am assuming that you would find that the greatest way to increase crew safety for such a Mars mission would be to shorten the time of the mission from under its current 2 to 3 year length, because 2 or 3 years in space dramatically increases the odds that something could go wrong and kill the crew.

    I would guess that an investment in multi-megawatt nuclear-electric propulsion, or some other realistically and economically achievable short-term propulsion option would be the best path to dramatically increasing the potential crew safety of a manned Mars Mission, because you would have the delta-V and transit times to cut a mission to under 6 months versus the current 2 to 3 years. I have seen studies that suggest that a 10 MWe class nuclear space reactor (weighing ~ 100 tons including radiators) would allow for round trips under 6 months and that it is feasible to build this within a 10-year time period for ~ $10 billion.

    What do you think?

  10. Pete says:

    My question is, is a fatality in the first 5-10minutes really 30x worse PR-wise than fatalities at any other time?

    It might be one rationalization of many, historically, it is where NASA has lost all of its astronauts, and they are sensitive to it.

    A much safer launch vehicle is not necessarily a bad idea, even if missions beyond LEO (to the real frontier) have far greater risk. LEO has been done enough for long enough that this part of the journey should have been fairly refined and safe by now. Getting to Everest base camp is proportionately far lower risk than getting to the summit.

    But with regard to long term safe routine transport to LEO, Ares I is an evolutionary dead end and so does not justify disproportionate investment in increasing safety – not that NASA seems to see that.

  11. Pete says:

    I have seen studies that suggest that a 10 MWe class nuclear space reactor (weighing ~ 100 tons including radiators) would allow for round trips under 6 months and that it is feasible to build this within a 10-year time period for ~ $10 billion.

    From what I hear solar power systems are already doing better than this (~170W/kg) and that the thin film solar being suggested for solar power satellites promises something like ~4 kW/kg (10MW/2.5ton). I am very interested in the potential nuclear rockets – but I would want to see much higher P/W ratios.

    I also hear that VASMIR is yet to demonstrate significant thrust (primarily a plasma generator at this stage), and has less performance (ISP and T/W) than existing Hall effect thrusters that are available in ~20kW sizes – many of which might be used in parallel. I have not seen good numbers on T/W for Hall effect thrusters or VASMIR, but I gather on the order of 1/10,000 that of chemical rockets. An electric rocket that could use say lunar LOX with an ISP of 1000 and a T/W of say 0.1 could be nice, any ideas?

  12. Anonymous says:


    You are correct that 4 kg/kw for solar-electric propulsion (SEP) are within reach of the Europeans and by DARPA’s FAST program, while current Nuclear-electric propulsion (NEP) schemes like NASA’s SAFE-400 program are in the range of 50 kg/kw. These are all focused on systems with power in the 10 kw to 100 kw range.

    NASA studies suggest that when we scale this to 1 MW to 10 MW systems that the NEP systems become competitive with the SEP systems by having specific power in the 1 kw/kg to 10 kw/kg range.

    The SEP systems do not scale well over 1 MW, because the launch fairing and deployment mechanism needed to carry a solar array that big starts to look silly.

    There are multiple options including VASIMR and gridded ion thrusters that can produce 4.5 newtons or 1 pound of thrust at over 3000 seconds Isp for every 200 kwe of power. A VASIMR with a ~ 12 MWe power supply supposedly goes one way to Mars in under 4 months. The thrust to weight (T/W) is closer to 0.0001 than 0.1.

    The point of my response to Jon’s post is to ask the basic crew safety question of the economics of investing more in NEP systems to lower the risk to the crew from the current NASA plan for a 2 to 3 year manned mission to Mars. A commercial 1-way manned mission to Mars can play with chemical propulsion systems, because crew safety is not the highest goal.

    A NASA led mission to Mars probably would not be credible, in terms of crew safety, if NASA continues to articulate an architecture that involves a 2 to 3 year round trip. The NEP option is probably not an option for NASA for crew safety, it may be a neccessity, because the only realistic mission scenarios, in terms of crew safety, probably involve round trips that are under 6 to 12 months.

  13. johnhare johnhare says:

    If you are after fast trips (within the reasonable budget predictions)to Mars, may I suggest one of the depot based varients. A top off to high mass ratio in highly eccentric Earth orbit, followed by an SSTO class perigee burn gives a 20 km/s max velocity with a 16-17 km/s Earth relative velocity in deep space. I’m pretty sure none of the high Isp systems can approach that in the near term.

  14. Anonymous says:


    Thank you.

    I am interested in analyzing the chances of the crew of a Mars mission surviving a 2 to 3 year mission versus surviving a 6 to 12 month mission. I do not know how to analyze crew safety on a Mars mission, but I would guess that a crew would have less than a 50% chance of survival in the Mars mission scenarios that last 2 to 3 years, because there are too many things that can go wrong in that amount of time. There also are very few abort options using the low delta-V chemical propulsion systems that would allow the crew to come home early if something went wrong.

    I think that I am really asking the question if NASA really has the political will to ever send a crew to Mars using their past DRM architectures that advocate 2 to 3 year missions, when the crew safety on these missions is likely to be unacceptable……Is NASA kidding itself when it thinks that it will ever be allowed to launch a crewed mission to Mars when crew survival probability might be under 50%?

    Dr. Mike Griffin said that his Ares-I and Ares-V architecture was designed to later allow for missions to Mars, but if we really look at the crew survival probability of Mars missions using the Ares-I and Ares-V architecture, we might find that this architecture could never support a Mars mission that meets politically acceptable crew safety standards.

    Ares-I and Ares-V might be poorly suited for Mars missions as well as lunar and LEO missions……especially if we look at crew safety.

  15. A_M_Swallow says:

    Crew safety on long missions – the ISS has been manned for 9 years without killing anyone, yet.

  16. john hare says:

    Fast trips would be good from several standpoints. I think that the mass spent for getting the speed might be more effectively used addressing the issues you consider dangerous. 6-12 month missions have plenty of time available to get a crew killed. I don’t see the relative danger that you do of 12 moths vs 36. I think the launch windows will be a more important factor than the propulsion methods used.

  17. Eric Collins says:

    ISS has been manned for nine years in LEO, where it is shielded from almost all of the high energy particle radiation and more than half of the electromagnetic radiation that an interplanetary mission would see. The ISS also has frequent resupply and repair/assembly missions, and the crew is only a few hours away from home if ever a significant emergency situation develops.

    A Mars bound crew is likely to be power and mass limited. They must survive the entire mission with only the spacecraft they leave Earth in, the parts and supplies they are able to take with them, and maybe some pre-positioned caches of supplies at Mars. This situation is incredibly precarious, and with our current level of space-faring technology, extremely ill-advised. We will need a considerable amount of technology development in closed loop life support, reliable power generation, radiation protection, and countless other little things that will impact crew safety and mission success.

    The research and development of these key space-faring technologies are all suffering from lack of funding at the moment. Many of them could be developed and tested on board the ISS if NASA wasn’t so preoccupied with developing its very own bright and shiny new rocket (TM). Imagine all of the advanced R&D that could have been accomplished over the last five years with $14 billion.

    When we say that NASA should relinquish its stranglehold on crew launch so that it can focus on doing the more challenging things, this is what we are talking about. The private sector is perfectly capable of, and indeed is on the cusp of, developing reliable crew launch capability. The private sector does not currently have the capacity, or incentive, to perform research into the effects of prolonged exposure to microgravity and radiation, nor does it have the experience performing on orbit assembly of large structures or the logistics of keeping a crew of astronauts properly provisioned for long duration missions.

    THESE are the real strengths that NASA should be playing to. These are the things which must be done, and only NASA and its international partners currently have the capability to do them. To insist that only NASA should be allowed to design and build the next generation of crew launch vehicle is selfish, short-sighted, and as Jon says, completely misses the point.

    Sorry for the long-winded rant. I realize that I’m probably preaching to the choir here, but I’ve been wanting to get that off my chest for a while now.

  18. Anonymous says:


    I agree with your rant.

    If NASA had decided to “commercialize” the Saturn-I, Saturn-V , Apollo, and SkyLab rockets, spaceships, and manned space stations in the early 1970’s instead of taking 40 years and spending $200 Billion building new rockets, spaceships, and manned space stations (i.e. Space Shuttle and International Space Station) that have less capability today than Apollo/Saturn/SkyLab had in the early 1970’s, then we would all be much better off. If NASA had spent a fraction of that wasted $200 Billion on US aerospace technology leadership over the last 40 years, then the US would be much better off.

    NASA is trying to make the same horrible mistakes that it made on the 40-year Space Shuttle and ISS debacle with the new Ares/Orion architecture.

    Most people do not understand that NASA could have commericalized the Apollo/Saturn/SkyLab architecture in the early 1970’s or at least allowed the US Military to use the Saturn-I instead of developing the horrible Titan IV rocket. After the sunk costs of the Apollo program, NASA could have easily commercialized Apollo and SkyLab in the early 1970’s, and put the United States decades ahead of other nations in multiple key space technologies.

    Imagine what the US Satellite TV industry could have been like if they had the opportunity to launch 6-ton GEO satellites in the 1970’s on commercial American Saturn-I rockets instead of 4-ton satellites on commercial Chinese, French, and Russian boosters in the 1990’s. The US commercial space industry designs satellites to fit on top of available rockets, and NASA’s decisions in the early 1970’s set even the commercial space industry back a decade or longer.

    NASA has done a true dis-service to the US Military and Commercial space industry since the 1970’s by spending a lot of US money on the wrong things. Hopefully NASA will not have the opportunity to do this to the US space industry for another 40 years with the Ares/Orion architecture.

    The US Government will eventually need to establish a new government agency to help DARPA with non-Military aerospace R&D if NASA is unable to do this job.

  19. Martijn Meijering says:

    Prepositioning propellant only requires small solar tugs, though preferably ones that can repeatedly cross the van Allens. Non crossing SEP tugs prepositioning hypergolic propellant can be done with today’s technology. Van Allen crossing tugs prepositioning cryogenic propellant or at least water which can be electrolysed at its destination can be done with near term technology.

    Plenty of ways to avoid HLV. But rumour has it Bolden has decided to recommend commercial crew taxis + NASA HLV for the exploration program. It doesn’t look as if we’ll get the high launch volume needed for RLVs, which is outrageous, but at least it looks as if we’ll get to keep the ISS + commercial crew for a long time.

  20. A_M_Swallow says:

    The space tug used to debug the Van Allen SEP’s sun light catches does not have to be the production design, it can be a tiny one. Sun light catches includes Stirling engines and other heat engines as well as coated solar panels.

    A Falcon 1e can lift about 1 metric ton to LEO. Tarous II a 5 tonne tug and Falcon 9/Atlas V a 10 tonne tug.

  21. Adam Greenwood says:

    My question is, is a fatality in the first 5-10minutes really 30x worse PR-wise than fatalities at any other time?

    It is a worse PR-threat to NASA’s continued operation. NASA can keep dinking around in LEO if something goes wrong on the moon, but if their ascender explodes they have to shut down their whole operation.

  22. Frank Glover says:

    I agree with Eric, especially as these problems (along with reducing long-term microgravity harm)…

    “We will need a considerable amount of technology development in closed loop life support, reliable power generation, radiation protection, and countless other little things that will impact crew safety and mission success.”

    …Essentially need to be solved only once (though we could expect continuing incremental improvements thereafter). When you have those solutions, they’re going to be pretty much the same, whether you’re in LEO, on a Moon base, carrying out a Mars mission, or (given advanced propulsion allowing a complete mission of, say, >1 year ) halfway to Pluto…

    But yes, almost anything you can do to shorten spacecraft flight times, clearly lightens all those burdens.

  23. Mike Long says:

    Why do people continually fault NASA for our perceived inability to do interesting things in space?.. really, I was in fourth grade when the first space shuttle launched and it was the single most defining moment in my life… I imagine it was the equivalent to July 20th 1969 for many of my older peers. Really, if you want to see the interesting things that NASA has done for aerospace, feel free to reference anything 20 years from now.. i.e.. x43.. enough said. Seriously though, I only have a couple of friends at NASA…


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