Random Thought: Dragon + Sundancer = CEV?

In a lot of conversations I’ve heard over the past year or so regarding COTS and its implications, many people trying to downplay the role of COTS (and explain why Orion has to be so heavy that only the Stick can launch it safely) have tried to play up the long duration features of the CEV. Basically they say “oh that Dragon capsule sure sounds nifty (if it ever flies), but it’s only capable of barely getting people to LEO, it doesn’t have all the features for exploration that the CEV does”. After all, it’s an exploration vehicle–it says so in the name!

Which is all well and good until you hear about what Orion doesn’t have. It doesn’t have a toilet (because nothing says exploration quite like Depends!) though it does have a “WCS”, it doesn’t have an airlock (so you have to depressurize the whole module if you need to do an EVA), and while much bigger than the Apollo CM, it only has about 19m^3 of volume inside (equivalent to a cube about 8.75ft on each edge, or smaller than the bathroom in my apartment complex). To be fair, it’s a lot more capable than the Apollo CM, or Dragon all by itself.

But all of that got me thinking about an idea I had a while back–combining Dragon and a Sundancer module for use as a long-duration space transport. So, I ran the numbers. Interestingly enough, once you factor in the fact that the Orion SM has to provide about 100-300m/s of delta-V just to make it to orbit (even with the CLV delivering them to -11x100km now instead of -30x100km), the CEV only delivers about ~1380m/s of delta-V once on orbit. Now, once you factor in extra propellants and tankage on the Dragon/Sundancer stack to bring its total delta-V up to that level (ignoring how much propellant Sundancer itself has because I have no numbers for it), the total “Initial Mass in LEO” for both designs are almost identical: ~51.7klb. The difference is that the Dragon/Sundancer stack could be launched on Falcon IX’s or Atlas V 401s.

Well, there’s that difference as well as the fact that the Dragon/Sundancer combo also get you nearly 10 times the interior volume (about the size of my 2-bedroom apartment), a toilet, and (I think) an airlock. Oh, and the possibility of taking 7 people instead of just 4. If I were going on a multi-week or multi-month trip to an NEO, you can be sure what I’d want to ride in.

Now, to be fair, there would need to be some changes to the stock Dragon/Sundancer combo for this mission. Dragon would need a beefed up heat shield (which is already in their plans), Sundancer might need a slightly beefed up life support system (since it’s only designed for three people for six months, it may not have enough “throughput” capacity to handle more than three or four people, and it is unclear how long Dragon could provide enough throughput for extra people), and there would probably be some communications and navigation upgrades you’d want for using those vehicles outside of LEO.

But it is interesting that they come out to such similar masses.

Now, one last thing. While a Dragon + Sundancer could probably be used as a CEV replacement, and could probably be used for a lower price than an Orion + Ares I, that’s not the optimal way to use it. You’d preferably not want to toss away the Sundancer module after every mission if you could avoid it, which leads you to entirely different mission modes, and technologies like aerobraking. But I’ll go into that more, some other day.

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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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15 Responses to Random Thought: Dragon + Sundancer = CEV?

  1. Anonymous says:

    Why again can’t we just put a US built Soyuz onto a Delta IV-H or Atlas V-H and inject it straight into L1?

  2. Gaetano Marano says:

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    as I’ve already posted on Hobbyspace… Dragon + Sundancer = BigelowOrion … 🙂

    http://www.gaetanomarano.it/articles/016_BigelowOrion.html

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  3. Brad says:

    Math error?

    […once you factor in the fact that the Orion SM has to provide about 100-200m/s of delta-V just to make it to orbit (even with the CLV delivering them to -11x100km now instead of -30x100km), the CEV only delivers about ~1380m/s of delta-V once on orbit…]

    Are you sure? I thought the CEV was supposed to have ~1,700 m/s of delta-V? But after subtracting 200 m/s you end up with only 1,380 m/s?

  4. Jon Goff says:

    Brad,
    When I plug in numbers for high end existing NTO/MMH thrusters, I typically get a high end of around 323-325s of Isp. With the most recent Orion mass numbers that I’ve seen, the total Delta-V I’m getting is only ~1580m/s. In order to get the 1700-1750m/s delta-Vs they were talking about previously, you either need to improve the mass ratio a bit or go LOX/Methane. Interestingly enough when I sub in a 360s LOX/Methane Isp number, I get close to the old Delta-V numbers. Not sure what exactly it means.

    I’m also not 100% positive about the propellant used for circularization. But from numbers I heard on NSF.com they seem to jive with the ~1400m/s “useable” delta-V number. I think I wrote up a spreadsheet for calculating stuff like that at one point, but that was a while ago.

    I’m also not 100% positive that my 10% dry fraction number for the additional tankage on the Dragon/Sundancer stack is realistic either. I think it is, as that’s actually pretty darned conservative for MR on hypergolic stages, but I could be wrong.

    Basically I was just amazed that the numbers appear on first blush to come out so close to each other. I could do some further digging around (to pin down the circularization delta-V, the assumed Isp of the CEV engine, etc) if you would like.

    ~Jon

  5. Ferris Valyn says:

    gaetano – the problem is infact that CEV is different than the Dragon – because its designed to be “exploration capable”, its more of a hodgepodge. Dragon is designed to do one thing basically, and one thing only – cheap access to orbit.
    Its a bit like the use of the LM as an alternative to direct landing ascent. In addition, there are 2 other problems you didn’t address – 1 – I am not convinced of your claim of easy inflation, and 2 – dealing with re-entry for that kind of vehicle. What is more intriguing (as Jon alluded to) is the new mission modes opened up for re-using the Sundance module – after all, why toss something that useful away after one use

  6. Brad says:

    [With the most recent Orion mass numbers that I’ve seen, the total Delta-V I’m getting is only ~1580m/s]

    Ah. What mass numbers are you using?

    I can’t seem to get a good fix on the Orion mass as various reports have numbers bouncing all over the map. I’ve seen the claimed CM mass anywhere from 7,500 kg up to 10,000+ kg!

  7. Jon Goff says:

    Brad,
    I’ll have to try scrounging up my source again, but the most recent numbers I’ve heard are: CM Mass– 10202kg, SM Dry Mass–4045kg, SM Prop 9186kg, and something like 650kg for the payload adapter (which I didn’t include in my Delta-V equations because it probably gets tossed early enough into the SM burn that it can be neglected, for the same reason I didn’t include the launch tower).

    If anyone has more up-to-date info, that’d be interesting.

    ~Jon

  8. Brad says:

    [the most recent numbers I’ve heard are: CM Mass– 10202kg, SM Dry Mass–4045kg, SM Prop 9186kg,]

    Yeah, I saw the same story.

    Just for curiousity’s sake, what delta-V would you come up with if the mass numbers for the CM and propellant were reversed? If the propellant was 10,202 kg and the CM was 9,186 kg? How close to the original NASA CEV requirement of 1,700 m/s delta-V would that get you?

    If reversing the numbers brings the CEV back in line with the original delta-V, maybe the article just made an error and transposed the numbers for the CM and propellant?

  9. Jon Goff says:

    Brad,
    It’s possible they had them reversed. Putting those numbers in puts the CEV up to about ~1800m/s Delta-V total, and about ~1500-1600m/s after circularization. I really don’t have a lot of super-secret inside sources on these things. But even if the numbers really are reversed, it’s still interesting how close to the numbers for a Sundancer + Dragon combo appear to be, especially figuring how much roomier, and likely more capable such a system would be.

    ~Jon

  10. Gaetano Marano - Italy says:

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    Ferris,

    my BigelowOrion has a single and simple purpose: transfer part of the heavy metal Orion’s habitable space to a lighter (small) inflatable module to have MORE internal volume with less total weight with a smaller (4-4.5 m.) Orion launched with a simpler, smaller and cheaper rocket

    about your points…

    1) the inflation mechanism I suggest is only one of may different possible solutions, and…

    2) the inflatable module is closed or jettisoned at re-entry

    the Sundance module can be “reused” in a moon mission only if… it’s leaved in lunar orbit OR it’s braked to earth orbit (adding its own engine and propellent) OR it’s deflated and re-entry on earth with its own (added) “case” and thermal shield
    unfortunately, the last two options are too expensive in terms of weight, costs and rockets to launch them…

    save a Sundancer may cost 10+ times the price of the module, then, the best/only choice is leave it in lunar orbit or use it once

    .

  11. Anonymous says:

    I thought Orion was going to reuse the toilet from ISS or the shuttle? If it’s not even going to have toilet then it’s a joke as even the little t/space CXV had a toilet.
    But dragon plus sundancer would make a great and mass efficient spacecraft only 20 tons for the entire craft minus EDS and LEM yet it would have more space then a salyut class station.
    If dragon proves successful and I think it will maybe it should replace orion.
    As for the 1380M/sec the Orion SM provides sundancer could be argumented to provide that as the station already has enough for large orbital altitude changes.

  12. Anonymous says:

    Mass comparisons

    It might be too early to do fair comparisons of mass between the Orion CEV, the SpaceX Dragon and the Bigelow Sundancer. The quoted numbers keep floating drifting, and you have to wonder how much PR is getting injected at this early stage.

    Once real-life flight hardware is built and measured, then we will see what vehicle is efficient and what vehicle isn’t.

    I will admit though I am very impressed by the supposed 14 cubic meters living space of the Dragon capsule. That makes the Dragon interior at least as large as the Orion CM.

  13. Brad says:

    D’oh! That last post was me! I forget to enter my name.

  14. Jon Goff says:

    Anonymous,
    I thought Orion was going to reuse the toilet from ISS or the shuttle? If it’s not even going to have toilet then it’s a joke as even the little t/space CXV had a toilet.

    I’m not 100% sure that the current configuration doesn’t have a toilet, but that’s what I had heard recently. A WCS system yes, but a toilet no. And yeah, that is pathetic if it turns out to be accurate.

    As for the 1380M/sec the Orion SM provides sundancer could be argumented to provide that as the station already has enough for large orbital altitude changes.

    I think so too. It’s not 100% sure, as Bigelow is even more tight lipped about design details than NASA, but it appears at this point that you might be able to make something comparable. Especially if it turns out that the existing propellant load for Sundancer is substantial (I treated it as zero for my current analysis since I didn’t know what the number was).

    ~Jon

  15. Jon Goff says:

    Brad,
    Yeah it is a bit early to prove one way or another which will be the best. I was just amused that right now the ideas were even in close competition capability wise.

    The reason Dragon has a lot of volume for its mass is because it uses a 15 degree cone instead of of the much steeper ~60 degree cone that CEV uses. CEV wanted to reuse Apollo data, while SpaceX is comfortable using something different.

    Another interesting thing to remember is that most non-first-orbit rendezvous missions to ISS actually take 2-3 days between launch and docking. Which means that most of these capsules *have to be* designed for as long of a transit time as one leg of a earth-to-moon-and-back trip.

    Just trying to inject some new thinking and ideas into things. Particularly trying to point out the idea that there are other ways to do exploration than a “CEV” capsule that tries to do everything, but does it at best in a mediocre fashion.

    ~Jon

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