Fast sketch of a two stage orbiter

[larrison]

This is just a fast sketch of something I've been kicking around for a while.

 

[spacefire]

of course it's nice, it's a lifting body <img src="/images/icons/smile.gif" /><br /><br />you're missing the giant LOX/LOH tank though.<br />Unless that orbiter has a really tiny payload mass fraction. <div class="Discussion_UserSignature"> <p>http://asteroid-invasion.blogspot.com</p><p>http://www.solvengineer.com/asteroid-invasion.html </p><p> </p> </div>

 

[mlorrey]

Yeah, the only way that vehicle could get into orbit with more than a postage stamp of payload were if it were airbreathing, carrying little LOX, and hydrocarbons rather than LH2.

 

[rocketman5000]

I am sure the people at NASA have studied this, but does anybody really know if the extra Isp that you get from H2 is worth the mass penality that you have with larger tanks? I suppose in a two stage system the mass penality isn't a problem, but a SSTO or TSTO I would assume you can't life an appreciable amount of extra cargo due to the weight of the tanks. Not to mention that Kerosene or other hydrocarbons would be much easier to make composited tanks for than Cyrogenic H2. I have only read of one or two companies that have mastered the construction of H2 tanks, and I think that the honeycomb sandwich has to be drilled so that it will allow the gases that leak through the inner composite layer to be extracted

 

[larrison]

Okay, the top picture is a sideview. The middle is the front view and the bottom is the top view. The goal is to basically repeat what Burt Rutan did on a much bigger scale. I didn't like the craft mounted under the "air breathing " first stage and I couldn't decide ona push or pull configuration so used both. A lifting wing in the front and in the back (built of carbon fiber of course). The first stage goes to 50,000 feet (maybe higher with boosters) then the second stage de taches and flys into orbit.

 

[rocketman5000]

For release purposes I believe that carrying your release craft under the "mother ship" is much safer as objects naturally want to fall espically if the angle of attack of the release craft isn't enough to produce positive lift <br /><br />also in a sketch such as yours it would be helpful if the two craft were of different colors. maybe trace over one with a pen, it would make the sketch much clearer

 

[larrison]

I hope this will make thing more clear.<br />I've been doing some research of current technologies that would be need for a project like this. Current lifting capacity smallest rocket to lift 2 ton paylode ect. ect....(the air bus weighs in around 450 metric tons the Russian rocket Strela, lifting capacity 2 tons, weighs in at 105 tons).<br />I believe we currently have the technology to build a two stage orbiter. The technology just needs to be matched up.

 

[scottb50]

The extra ISP is well worth it. Just because it is physically bigger to contain LH2 doesn't have to add that much mass. You have to deal with LOX and dealing with LH is Basically the same, the engine is pretty much the same, so might as well go with the one with the most capability.<br /><br />Having a, hopefully, inexhaustable source of water to work with, the oceans, it seems a better source of power than fossil fuels anyway. Just my opinion. <br /><br /> <div class="Discussion_UserSignature"> </div>

 

[mlorrey]

<blockquote><font class="small">In reply to:</font><hr /><p> does anybody really know if the extra Isp that you get from H2 is worth the mass penality that you have with larger tanks?<p><hr /></p></p></blockquote><br /><br />It isn't. NASA plays with hydrogen and promotes it purely for environmentalist reasons, to win the votes of senators and congressmen for its budget who rely on environmentalist constituencies. There is no rigorous scientific argument for LH2 as a superior SSTO or TSTO propellant.<br /><br />The below referenced papers demonstrate pretty clearly that LH2 is actually a terrible fuel. Capt. Michael Burnside Clapp has also written a number of papers and comments on the issue.<br /><br />Dr, Bruce Dunn's papers on alternate propellants:<br />http://www.dunnspace.com/alternate_ssto_propellants.htm<br />http://www.dunnspace.com/isp.htm<br /><br />Some of Clapps comments:<br />http://yarchive.net/space/rocket/fuels/hydrogen_deltav.html<br />http://64.233.187.104/search?q=cache:dYiqYOpi5V0J:webhome.idirect.com/~earlcp/messages/M1168.HTML+burnside+clapp+LH2+kerosene&hl=en<br />http://64.233.187.104/search?q=cache7xpqzU_S9YJ:webhome.idirect.com/~earlcp/messages/M1123.HTML+burnside+clapp+LH2+kerosene&hl=en<br />http://sworld.com.au/steven/pub/lrb.pdf<br />

 

[mlorrey]

<blockquote><font class="small">In reply to:</font><hr /><p><br />The extra ISP is well worth it. Just because it is physically bigger to contain LH2 doesn't have to add that much mass. You have to deal with LOX and dealing with LH is Basically the same, the engine is pretty much the same, so might as well go with the one with the most capability. <br /><p><hr /></p></p></blockquote><br /><br />Actually, the very poor density of LH2 is the primary problem causing the mass fraction difficulties of various SSTO projects. W/ LH2, you need at least a 92% mass fraction of fuel to do SSTO, but the density of LH2 is so low that any LH2 tank is going to equal a major fraction of the LH2 fuel itself, typically about 1/3.<br /><br />Simple minded engineers look at the BTU/kg capability of LH2 while completely ignoring the terrible BTU/liter. While LH2 has twice as many BTU/kg as, say, methylacetylene, MA is more than six times denser, resulting in a comparative advantage of three for methylacetylene.<br /><br />It is possible to do SSTO with LH2 and LOX, but ONLY as an expendable launcher. For example, the Shuttle ET, equipped with five or six SSME engines under it, could put about 30k lb in a 200 mile orbit, but the launcher would be entirely expendable. You could save all but one of the engines by dropping them as part of a recoverable pod when 65% of the fuel is burned, just like the early Atlas dropped two engines for Glenn's Mercury capsule. This would also increase the payload in orbit to about 60-70k lb. Such a launcher would be a really good alternative to the currently planned two stage SRB/liquid launcher for the CEV. The ET would then be very useful as a module for space station and other orbital construction projects. With a built in maneuvering system needed for such a launcher, the ET would no longer be a drifting obstacle.<br /><br />This all being said, building a reentry system and TPS for this sort of launcher would eat up all of the cargo capacity, all because of the choice of f

 

[rocketman5000]

Very nice post. Basically what I was thinking about when I ask the question. In a reusible vehicle I would think that you would want it to be as small as possible to eliminate paying for the launch and recovery of a TPS any more than needed. If only we could Star Trek it and ignore the need for a TPS. Anyone have a sheild against Plasma?? <br /><br /><br />Kinda reminds me of the advantages you can acheive with a deisel through the increased compression ratio. When exaimed at an energy per mass or at the same compression ration gasoline clearly is the more efficient fuel. The practical application is much different however.

 

[scottb50]

If you use an LH2/LOX first stage that faces roughly the same re-entry heating as SS-1 the TPS requirements are pretty low. Maybe not Star Trek, but a lot simpler than SSTO.<br /><br />True the bulk of the of the vehicle is bigger, but since most of it is empty volume the basic weight would not be a whole lot higher than a hydrocarbon version. <div class="Discussion_UserSignature"> </div>

 

[rocketman5000]

I was reading the links you provided and I came up with a question I couldn't find an answer to. The articles talk about accounting for the backpressure changing the value of Isp throughtout its accent. My question came when using an aerospike engine. Since the area ratio constantly changes throughout the accent does the exit velocity remain constant and therefore have a constant Isp? Doesn't seem like it would to me. Seems like the Isp would constantly rise throughout the accent

 

[mlorrey]

<blockquote><font class="small">In reply to:</font><hr /><p>If you use an LH2/LOX first stage that faces roughly the same re-entry heating as SS-1 the TPS requirements are pretty low. Maybe not Star Trek, but a lot simpler than SSTO. <p><hr /></p></p></blockquote><br /><br />This is a very good point: a TSTO could recover the first stage (just as I suggested above recovering all but one of the SSMEs in my proposed SSTO (actually Gary Hudson proposed it first)) You don't need a serious TPS when your first stage is peaking at less than Mach 10. You do, however, need some serious structural reinforcement beyond the typical rockets axial compression load bearing structures. An LH2 tank, being more than twice as large as an RP-1 tank of equal payload-in-orbit capability, is going to encounter an exponentially greater amount of lateral aerodynamic loads, particularly in the hypersonic range on reentry.<br /><br />Eventually you wind up with the same/similar problems the dinosaurs faced in their size-race.<br /><br />But your upper stage IS going to need a serious TPS. Maxing out surface and cross sectional area (as was planned with the X-33) is a good way to reduce reentry heating to the range of more conventional materials, but it adds aerodynamic loads in the launch phase that increases fuel demands.<br />

 

[mlorrey]

Nozzle exhaust velocity (all else being equal) is a function of the difference between the combustion chamber pressure and the ambient outside pressure, and how efficient the nozzle translates from one to the other. As outside pressure drops, you get higher exhaust velocity due to the increased pressure differential.<br /><br />An aerospike allows optimum Isp at all altitudes because the atmosphere itself makes up most of the 'nozzle': as atm press changes with ascent, your exhaust expands outward according to the gas law in the optimum bell shape. It doesn't maintain constant Isp, just the optimum possible for that altitude and fuel mixture. The inner spike and the atmosphere work together to produce thrust. There are some good aerospike pages on the web that are easy to google that explain it better than me.<br /><br /> Essentially a Bell Nozzle engine is designed for top Isp or thrust at one specific altitude. With an SSTO or other vehicle operating the same engine at all altitudes (like the Shuttle), you design it to optimize in vacuum. NASA engineers have learned to cope with this problem in the SSME by adjusting the fuel mix and throttle to provide some altitude compensation.

 

[mlorrey]

I'd also like to comment on the idea that big fuel tanks are somehow a plus for an SSTO/TSTO: they aren't, simply put. Beyond being a significiant aerodynamic drag, they really aren't worth saving that much. Tanks are cheap to build and are of simple construction. Why would you build an expensive TPS to recover a tank that is worth maybe 1% of the cost of the TPS? You should only focus recovery efforts in your RLV design on recovering the parts that are expensive: crew cabin, engines, guidance. Besides, a tank is a lot more useful in orbit than falling into the ocean. Big fuel tanks can be used as space station modules.<br /><br />The STS threw away 114 ETs into the ocean, like empty soda cans thrown out along a highway. They aren't worth much here on earth, but they are of inestimable use in space, because there isn't anything else there. <br /><br />Lets use the Conestoga Wagon as an example. Did the western settlers, once they'd gotten out west, just throw their Conestogas away? No, they used the wagon as a farm wagon, the canvas tarp was used first as a temporary roof on their cabins, and later for mattress materials, among other things. Settlers didn't take along things that were disposable, they brought things that were durable and could be used for more than one purpose, and they sure as heck didn't send those Conestogas back to the East Coast.<br /><br />Today the space station produces tons and tons of trash every trip. The STS throws its ETs into the ocean, and RLV LH2 proponents propose building these humongous fuel tanks for their Green Dream launchers, but sending them back to earth with a frightfully expensive TPS that is more expensive than the tanks themselves. The logic just doesn't add up.

 

[rocketman5000]

fuel is by far the cheapest of all the spaceflight ingredients. A TPS made of more conventional materials would be a great payoff for more fuel. Like stated above denser materials may help to reduce some dry weight and therefor the TPS requirements.

 

[rocketman5000]

I acutally understand both concepts very well from a flow standpoint and exit velocity, but I'm not as well versed in terms of Isp as my compressible flow training was in mechanical terms rather than aerospace.

 

[mlorrey]

The fuel itself IS the cheapest of all the costs, IF you just count the cost of the fuel itself. You need to calculate the systemic costs of your fuel choices, though. Cryogenics, for instance, impose higher costs than non-cryo fuels. Low density fuels impose lots of size costs that affect the whole program (since there is a very close relationship between vehicle size and cost), in addition to aerodynamic costs that also result in more fuel and therefore larger vehicles.<br /><br />Arguing about $0.50/kg for LH2 vs $6.00 for MAPP or RP-1 is irrelevant if you don't figure in how the fuel choice impacts the whole vehicle design and operations.

 

[rocketman5000]

I think we are saying the same thing. What I was stating that using more mass of fuel will probably be advantageous if it could lead to a smaller vehicle with less TPS et cetra.

 

[mlorrey]

Yes. I happen to like the GTX concept that NASA was working on, though I think it should be developed using a hydrocarbon fuel of some sort. The Hydrogen version was envisioning a 180' long vehicle capable of putting 600 lb in orbit. Halving aerodynamic losses from vehicle size would give thousands of lbs in payload additional.

 

[mlorrey]

I am wondering how many folks here are actually interested in and capable of joining in a start-up space venture. I've got an idea for a vehicle that should be pretty affordable for a private venture to develop, even without Paul Allen money, that would be a reusable suborbital tourist vehicle, or a reusable first stage for a launcher capable of putting 100-200 lbs into orbit.

 

[rocketman5000]

I would be a go. I would have to know more about your proposed vehicle though. That and the structure of the company. I believe if you work smart instead of working hard a lot can be accomplished. I did preliminary design studies from Nov. last year till late April this year of several concepts. PM me if would like to talk more<br />

 

[mlorrey]

sent you a pm, but the system doesn't have a record of it....

 

[rocketman5000]

I got it. I'll be send you something back shortly