Orion II

guest blogger john hare

The multiple problems of solid rocket first stages would lead one to believe that the people that specified them would change their minds after they sobered up. That not being the case, it is somewhat interesting to think of ways to make it work anyway. The primary problems seem to be, excessive vibration, catastrophic failure modes requiring robust escape systems, control on all 3 axis, and poor scaling.

Apparently the upper stages and interstages are going to be tasked to handle most of these shortcomings. This Orion II idea is in response to people commenting on the Aries II idea. I agree that Direct, EELV, Falcon 9, depots, and a hundred other approaches are better than der Griffenschaft, but it is possible that the country will remain stuck with it. The context here is not supposed to be a better vehicle than the competition, but rather a way to get some lemon juice if even lemonade is not available.

Orion II

Place an over sized H2/O2 tank on top of Aries with low pressure gas generator driven pumps pushing both propellants into the small 3rd stage tanks on Orion. The Orion rests on shock absorbers between the large tank and its’ RL10 clusters. Outboard of the stack are two or more large H2/O2 engines that light on the ground before Aries ignition. The large engines have sufficient thrust to keep the shock absorbers in tension throughout the Aries burn. The secondary function is  enough thrust to make up the performance shortfalls of the solid first stage.

 Three axis control is also supplied by these engines both during Aries first stage and their independent second stage burn after Aries drop off. In case of abort, the second stage tank becomes the shrapnel absorber while the Orion accelerates away on the large engines using the propellant that would have been used for the RL10s in a nominal mission. On a nominal mission, the large H2/O2 engines are dropped when the second stage tank is depleted, leaving the third stage with a full propellant load for its’ onboard RL10s.

The large propellant tank provides one layer of shock absorption from the solid rocket shaking. The large H2/O2 engines have enough thrust to keep the Orion clear of solid contact with the tank during the solids burn for a second layer of protection. The tensile shock absorbers between the tank and the Orion are the third layer of protection and should be capable of eliminating all but the most violent shaking.

The large H2O2 engines suffer considerable performance losses due to being canted outboard. These Isp losses on the order of 5% may be not too high a price to pay if it is necessary to save the concept. Gimbaling these engines can control the whole stack without much problem considering the relative sizes. During the first stage burn, they make up for the possible under performance of the Aries by providing several hundred thousand pounds of higher Isp thrust that would not normally be available to the concept. After Aries separation, they have enough thrust to carry the partially depleted second stage tank and the Orion spacecraft to near orbital velocity.

In case of abort, the second stage tank remains attached to the Aries to absorb shrapnel, while the large engines accelerate the bare spacecraft away using the onboard propellant that would have been used for the RL10s during a nominal mission. The large engines have enough thrust to escape at 4+G because they are sized to keep Orion clear of hard contact with the lower stages and carry the partially full second stage tank during a nominal mission.

On a nominal mission, the large engines are dropped with the second stage tank leaving the spacecraft to continue with the reliable vacuum rated RL10s. Internal tankage and number of RL10s would depend on final design details. One possibility is that the whole stack could be optimised for a lunar mission with abort to orbit on RL10s possible.

With the extra performance and escape routes available, this upper stage/escape system/spacecraft could be placed on the Atlas or Delta launchers with sufficient confidence to guarantee that either of them could perform the missions. With the safety aspects of the inherent escape system, relatively early flights of the Falcon 9 could do the job. Up and coming launch providers could be used as available and desirable for unmanned resupply at fairly early stages in development.

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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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8 Responses to Orion II

  1. jsuros says:

    What if you extend the engines out on a boom once the solid stage drops away so that you could eliminate the cant angle? You would get the performance back for the greater upper stage velocity increase at the cost of some structural hardware. The Roton design (and your own spinning detonation buckets) took this sort of idea to a logical extreme.

  2. Eric Collins says:

    So, let me see if I understand this. In order for the capsule to be kept in dynamic tension with the first two stages, the upper stage engines would have to be powerful enough to carry the entire weight of the capsule and service module plus some extra margin. Then, the SRB is really only carrying it’s own weight and some fraction of the weight of the second stage. After first stage separation, these same upper stage engines continue to fire, but are now carrying what’s left of the second stage mass in addition to the capsule/SM. So, do you have any idea just how much mass that would be, and consequently, just how powerful those upper stage engines would have to be?

    Apparently, this idea is not too far fetched… witness the lack of folks commenting on the holes in the concept. As for myself, the only thing I could think of is the thermal interaction of the side mounted engines with the second stage tank. You would either have to have some fairly beefy heat shielding there, or else you would need to cant the engines way out. Either way, you’re talking about a loss of efficiency which may turn out to be non-trivial.

  3. Eric Collins says:

    And one more thing. The upper stage engines are also the abort motors, but in case of an abort the second stage tank is dropped along with the first stage. This requires you to pump your cryogenic fuels from the second stage to the service module while in flight so that there is sufficient propellant in the tanks to accomplish a safe abort. I’m no rocket plumber, but I can’t imagine that will be an easy or efficient system to implement. Perhaps Jon can comment on that.

  4. jsuros says:


    The engines on every second stage need to be powerful enough to propel the capsule, it’s service module, and the fuel tanks of the stage for a period of time (100+ seconds). John’s innovation is to use the engines to pull rather than push the second stage. The five second supply of fuel in the service module allows the second stage tanks to be dropped in case of emergency while the five seconds of fuel separates the capsule and service module from whatever disaster is occurring below the second stage tank.

    As to the plumbing used to pump fuel (and oxidizer) to the engines, think of a drinking straw. The pressure in the second stage tanks (see “gas generator lift pumps” in the diagram) pushes the fuel and oxidizer up the tubes against the direction of acceleration of the rocket.

    Your comment about thermal effects of the engines firing against the second stage tanks is a good point. Maybe it will help pressurize the tank? Maybe the effect will turn the second stage tank into something like a plug nozzle?

    I doubt any amount of lipstick will save this pig, but the idea seems sound.

  5. johnhare john hare says:

    The second stage/abort engines would have a thrust 4 times the mass of the fueled upper stage. If the engines provide one million pounds of thrust, then the upper stage can mass no more than 250,000 pounds. The upper stage plus second stage tank and its’ remaining propellant can mass around one million pounds. The upper stage mass and drop tank would go up or down depending on the engine choice.

    Having demonstrated considerable ignorance of the SSME, I left that part alone. There would be a minimum allowable mass dictated by the thrust of the SRB. HH was trying to explain that part to me in the last post.

    The heating of the drop tank would be a major issue. Whether it would require booming out the engines or adding tank insulation would require considerable thought.

    It could be that this idea is so far fetched that most serious commenters are too busy laughing.

    The second stage drop tank would make a dandy propellant depot with pumps and handling gear already installed.

    As for the quantity of lipstick required for this pig, we need to solve the viscosity problems for a lipstick turbopump, we have a customer.

  6. Habitat Hermit says:

    I cannot speak for others but my brain was (and partially still is) stuck in the last post. This blog has always had and continues to have a great deal of challenging ideas that really get the gears moving.

    I think I understand Eric Collins’ thinking but this ought to work. Thinking out loud the shock absorbers are stiff enough to not respond until receiving greater linear force (from vibration) than normal acceleration would supply, when the 1st stage and 2nd stage main tanks go beyond that level the vibration is absorbed down to an acceptable level by the shock absorbers which are continuously assisted by the above liquid engines providing a pull (any value should help and it must not be too large or the vibration won’t be smoothed out). In other words rocket assisted shock absorbers which should be more responsive in terms of time needed to regain absorption potential and more efficient in relation to their own mass.

    This is sort of a reconfiguration of a combination of the active rocket dampening and the shock absorbers that NASA has looked at for Ares I, and also the LAS function. I’m not sure it solves or helps with other issues though.

    That’s as far as my brain has got (I might not have understood things correctly and all errors are mine) and it needs a break now ^_^

  7. MG says:

    A couple thoughts:

    1. I can see how this idea *could* help with longitudinal vibrations. What about lateral and torsional vibrations?

    2. IIRC, the SRM is already underpowered. How does adding upper stage mass helps achieve orbital velocity?

  8. johnhare john hare says:


    1. I hadn’t thought about those two modes as being as much of a problem. I’ll think about it and see what I come up with.

    2. There are two or more fairly large liquid engines burning from the start, which could be upwards of a million pounds more thrust.
    2A. The two SRB solution from the previous post could solve the under power problem with a lot less development cash.

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