Aries II

guest blogger john hare

I have been reading about some of the financial  numbers and technical problems of the Aries I for the last couple of weeks with more interest than usual. The idea that $8B has been spent already, and that total cost to first flight is projected to be $35B just boggles my mind. The laundry list of technical problems from under performance to extreme vibration should have stopped the program even before this price tag became known to NASA management.

If we accept as given that a shuttle derived vehicle with solid rockets was the only politically acceptable choice at the time, was it possible that something better could have been chosen? Something that would keep much of the shuttle work force and contracting organization together as possible? As a basher of der Griffenschaft, it seems possible to me that a somewhat similar architecture could have done better.

Suppose that instead of stretching and totally redesigning the SRB, they had shifted to a two SRB first stage with the exact same units as used for the last hundred and something shuttle launches. These rockets are fully developed and tested with an extensive flight history of operating in pairs over the last three decades. The purchase costs, handling , and performance are known quantities. Development consists of building an attachment structure, upper stage adapter, and vibration dampening gear. With the considerably more lift performance available from eight segments compared to five in Aries I, the problem fixing payload hits could be absorbed without sacrificing the flavor de jour safety systems NASA would like to have. They wouldn’t even have to game the requirements to match the competition from ULA, Direct, and various upstarts. While it’s possible that this would cost as much as the projected Aries I, it shouldn’t, and if it did, it would be for a system nearly twice as capable. 

The Aries I upper stage has another interesting budget feature in development of the J2S. This was supposed to be a simple upgrade of the flight proven J2 of Saturn fame. Now it seems to be a major development project in its’ own right. If the two SRBs were used instead, the upper stage would be much larger, perhaps too large for even the upgraded (read new engine) J2S. SSMEs, for all their expense, have a lot more flight history than the original J2 ever had. Modifying an SSME for second stage use would involve a new ignition system that would work in vacuum, and a much expanded nozzle for improved vacuum performance. Though SSMEs are expensive, a lot of them could be bought for the development price of the J2S, and the payload to orbit would about double.

Aries II

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johnhare

johnhare

I do construction for a living and aerospace as an occasional hobby. I am an inventor and a bit of an entrepreneur. I've been self employed since the 1980s and working in concrete since the 1970s. When I grow up, I want to work with rockets and spacecraft. I did a stupid rocket trick a few decades back and decided not to try another hot fire without adult supervision. Haven't located much of that as we are all big kids when working with our passions.
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28 Responses to Aries II

  1. Jon says:

    I’m not sure what the development costs for just Ares 1 are at this point, but I suspect that despite the extra costs of the double boosters per flight (I don’t know what they cost off the top of my head) simply cutting the development costs for the 5 segment booster out of the equation will more than pay for the extra per-flight monies.

    I don’t care to comment in detail on the SSME vs. J-2 debate because rocket engine modification and development costs are not something I’m intimately familiar with. My gut tells me, however, that the savings for your solution might not be as much as you think, but the extra payload would make it worth it.

  2. MG says:

    IIRC, ATK has done chart-o-studies of multiple SRB-based orbital launchers.

    I don’t understand what this gets you beyond a LEO launcher, though. Why not just go with what the DIRECT folks have proposed, IF we are going to use existing STS hardware and infrastructure?

  3. Martijn Meijering says:

    Wouldn’t this make thrust oscillation problems even worse?

  4. johnhare john hare says:

    IIRC, ATK has done chart-o-studies of multiple SRB-based orbital launchers.

    I don’t understand what this gets you beyond a LEO launcher, though. Why not just go with what the DIRECT folks have proposed, IF we are going to use existing STS hardware and infrastructure?

    I agree that this would still be a pig, just possibly a politically acceptable pig considering the orriginal driving force behind the current mess.

    Wouldn’t this make thrust oscillation problems even worse?

    Probably would, but with so much more mass margin available, solutions would not cut into payload as bad.

  5. Eric Collins says:

    IIRC, the problem with using the SSME’s on the second stage was not so much with vacuum ignition or vacuum performance as with trying to light them while in free-fall. I remember listening to someone give a presentation about SSME vs. J2X back in the early days of ESAS. The thing that has stuck with me about that talk is that this guy said at one point that the thought of doing a mid-air ignition of an SSME kept him awake at night. It just wasn’t designed to do that. It was designed to be lit while sitting on the ground, under a full 1G load.

  6. Martijn Meijering says:

    Another possible politically acceptable pig was mooted by Aerospace in their EELV as Ares I replacement presentation before the Augustine commission: AIUS or an J-2X powered upper stage on EELV.

  7. Harlan says:

    Have you estimated the G forces during liftoff on that thing? I’m guessing that they’re prohibitive for the crew…

  8. Jon Schneider says:

    IIRCC, the reason the Ares booster has escalation problems is because it’s a solo booster. On the Shuttle the escalations of the two boosters cancel one another out. Or at least that’s what I heard.

  9. johnhare john hare says:

    Eric,
    I’m thinking, I’m thinking, it’s not like I take being wrong gracefully. 🙂

    Martin,
    There are a lot of solutions better than the current one. I was just throwing something out there that could have solved many of the problems with less time and money.

    Harlan,
    Control G forces by increasing the mass of the upper stage, usefully if possible, with ballast if not.

  10. MG says:

    Mr. Schneider,

    The STS stack absorbs the SRM vibrations. When fueled, it is a massive vibration absorber. The Griffenschaft does not have comparable absorption capacity.

  11. Habitat Hermit says:

    I’ll second Harlan’s comment and expand upon it.

    I’ve though a little bit about a 2×4 segment Ares I (because it seems like a reasonable possibility at first and is a “naturally logical” alternative before one discovers why not) and Harlan’s objection is one of several issues that make it unlikely to be realistic or –at the end of the day– cost-saving. Straightforward ballast won’t on its own solve the issues (point 1 and 2 below).

    Now I’m not a rocket scientist but I feel (perhaps too) confident about the following, and it’s pretty damning to Ares I.

    1. The 2 SRBs provide about 60% of the force needed for the STS stack and a new utilization without the main tank and Shuttle takes away the two heaviest loads that they carry (one of which is _dynamic_: the total weight of the fuel in the main tank decreases over time all the way from liftoff). Thus for any other than existing use the acceleration, thrust, and/or total power is guaranteed to be (most likely severely) “misaligned” one way or the other during one or several parts of the journey unless one duplicates the ratios of change (and I’m willing to bet that won’t be easy nor efficient nor cheap).

    When speaking of solid fueled rockets the normal solutions to such challenges is to change the fuel geometries (both “internal” and “external”) which is precisely what has happened with Ares I (both have been changed) and in addition the fuel composition can be changed and this has also been done with Ares I.

    Changing only one of those three things would alone be enough for it to be a new solid fuel rocket design and rocket.

    Result: little, no, or a negative amount of money saved no matter if one goes for one stick, two sticks, or any sticks.

    2. A complicating factor is that the main shuttle tank also acts as a vibration dampener _not only_ because of it’s mass but also (something I haven’t seen anyone mention anywhere else) because the contents of the tank are liquids with some freedom of movement. It’s exactly the same principle as the huge water tanks often (always? usually?) suspended on the top floors of skyscrapers to lessen and counteract the swaying movement of the buildings.

    So the “alternatives” continue to be:
    1. Change the SRBs into new rockets.
    2. Create very elaborate dampening and/or ballast systems.
    3. Both 1 and 2.
    4. Something entirely different.

    I do think you take being wrong gracefully John Hare and hopefully I will be as good if/when the next person comes along and shows me wrong ^_^

  12. Chris says:

    Better to make the second stage tank bigger, attach the SRBs to that, and ignite the second stage engine on the ground before the SRBs to ensure it is working. I have in mind a stage that is the same size as an external tank, because that sized tank has already been shown adequate for damping of SRB loads, and for propulsion using two or three dirt cheap RS-68’s.

    With ground starting your isp sucks, but tank and fuel is cheap and you need it to deal with thrust oscillation from the solids anyway.

    I’m fairly certain that no one has thought of this totally awesome idea, so feel free to call it the ‘CHRIS launcher’ of CHRIS for short.

  13. Habitat Hermit says:

    Hah and “CHRIS”/Direct actually proves me wrong since it both sufficiently duplicates the current use of the SRBs including the vibration dampening and is likely to be cheaper. So I was wrong earlier (never looked at Direct that way before). Easy come easy go ^_^

  14. Rand Simberg says:

    One other benefit is that, with two motors, the first stage can do its own roll control, and relieve the second stage of the (onerous) requirement of having to roll the whole stack.

  15. Rand Simberg says:

    On the other hand, thrust asymmetries could be a big problem…

  16. I have spoken to rocket scientists about the idea of two shorter SRBs and Harlan is right the acceleration is not good for the crew. I’ll have more to say about Augustine et al during the course of this week. If anyone cares… 😉

  17. johnhare john hare says:

    Unlike the vibration problem, the acceleration can be handled by sizing the upper stage appropriately. It is not like extra mass cannot be put to good use in some form.

  18. Habitat Hermit says:

    Yeah but the acceleration from solid rockets is fully dependent upon the geometries of the solid fuel. And changing those geometries makes a new rocket. Ignore those facts of solid fuel and one walks right into the same trap Dr. Griffin walked into.

    Some of those geometries in the existing SRB design _change_ along the length of the SRBs (talking _before_ ignition and burn) in order to be tailored to the vehicle/use in question.

    In the case of the SRBs they are tailored to the mass and change of mass including the dynamic change represented by main tank fuel as well as the dynamic change represented by the SRBs themselves (not just weight). They are also tailored to the flight path.

    Solid fuel rockets are all about burn rates.

    I wonder if I’m able to make the point clearly, is it understandable? To me this seems like very basic solid fuel knowledge yet I don’t seem to be able to get the point across.

  19. David Summers says:

    I think the real issue here is that the vast majority of space launch costs are R&D and people. You cannot get rid of people in a government operation, so your only hope is to cut R&D costs. That means, simply, use what you have.

    So I like the idea of reusing the solids – exactly as they are. Instead of telling the engineering team “we want to lift X, design us a rocket system,” they should say “we want to lift X, using our existing SRBs and engines – design a rocket system around them.”

    The designed rocket would have “terrible” performance. For example, to address the SRB thrust curves being wrong a huge tank of water would be added to the design. As the rocket goes up, the water is thrown overboard at the rate required to keep the thrust at the correct point. That means your rocket would be easily twice as heavy as required for the job… but that doesn’t matter! The fact is, mass costs nothing. Propellant costs nothing. New major systems are impossible to get at any price! We just do not have the capability / political will. Billions will be spent, programs will appear and disappear, but nothing will be created.

    If you want to lift X, design your rocket to lift 2X. It is easy to throw away unneeded performance after the design is done.

  20. johnhare john hare says:

    Habitat,

    I believe your point is that the current SRBs are very specifically tailered the the Shuttle stack as it currently exists and to bolt them to any other stack would leave them mismatched to the application.

    My point is that the thrust of the current SRBs are well known throughout the flight profile and that the new upper stage would need to be tailered to that instead of starting over as in der Griffenschaft. With the exact thrust and mass of the SRB known at any given second, it would seem that the upper stage could be designed to match that thrust profile. I believe that some mismatch could be tolerated. It’s not like the astronauts are going to unexpectedly experience 8 G.

    I believe that to redesign the solid to the extent currently being done is more difficult than designing a whole new liquid booster. I believe that license building RD170s and designing a new first stage around two of them would be much cheaper and far more capable than this kludge.

    Sometimes we talk past each other, but we seem to converge after a while.

  21. Habitat Hermit says:

    I apologize if I sounded/was too harsh and I do realize that this is an effort to make the the best out of a disaster and to do so with very constrained (yet sadly realistic) political parameters in a “what if?” rewind back to the start of ESAS/Constellation.

    Here is a chart of the SRB thrust over time normalized to sea level pressure: http://en.wikipedia.org/wiki/File:Srbthrust2.jpg

    The big valley in the graph is likely all because of Max-Q.

  22. anon says:

    John

    It’s almost impossible to air-start a SSME. It’s a 120 Ton payload to make it start.

  23. johnhare john hare says:

    Just estimating from the chart, at about 80 seconds thrust is 5M lbs for the two units while mass is probably around a third of the initial value. If the remaining SRB masses total 800,000 lbs, the the upper stage and various gear other than the boosters must mass a minimum of 867,000 lbs to hold the experienced Gs under 3. Or 450,000 lbs if 4 G is acceptable.

  24. Rhyolite says:

    Two thoughts:

    Does anyone have promotional material from ATK’s EELV bid circa 1996? If I remember correctly, they proposed clustering up to three shuttle SRBs. I wonder if they published performance data for those concepts.

    One of the justifications for Ares I is that it reduces the development cost of Ares V. Presumably one of the contributions is the 5 segment SRB. Taking a page from John’s concept, I wonder if the Ares V development could be made cheaper by using four unmodified 4 segment SRBs. We might call this new vehicle Ares VI. I would think the additional thrust would allow the liquid core to be smaller and more manageable to develop, perhaps even small enough to be derived from the shuttle ET. I recall seeing concepts along these lines in the 1980’s so it is hardly an original thought.

  25. Tom D says:

    For what it’s worth LM seems to have noticed this discussion and has included it in their internal news.

  26. johnhare john hare says:

    Tom D,
    It’s nice to hear that LM employees have a sense of humor.

  27. Tom D says:

    I just hope that nobody in power decides that we really need to use more SRBs…

  28. johnhare john hare says:

    If they do, then we have been giving aid and comfort to the enemy. 🙂

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