new launch vehicle

nacnud · Jul 28, 2005

Why, the DC-X was a technological demonstrator. A cheap one at that.

hurricane4911 · Jul 28, 2005

Before DC-X, there was the Apollo LEM. The 2 stage LEMs were excellent performers, in a very weak gravity. Viking was another good example. 15-20 years of service has obviously taken it's toll on the shuttle fleet. It was a good idea in the 1970s, however, the system is just not reliable anymore. NASA knows this. Shuttle-C is a good idea. The question is can this be developed in a time frame that would allow completion of the ISS? As for human spaceflight, until we achieve and prove another technology, a cone shaped capsule on top of a 3 stage giant gas tank is proven, reliable, and safer.

no_way · Jul 28, 2005

I'd appreciate if you pointed us in the direction of where did you do that. A specific thread somewhere ?

spaceinator · Jul 28, 2005

In responce to: <hr />Shuttle-C is a good idea. The question is can this be developed in a time frame that would allow completion of the ISS?<hr /> I think it can be completed in a reasonable amount of time. The question is will it. NASA has a huge budget compaired to other aerospace companies--it just needs to put all that money in the right place.

propforce · Jul 28, 2005

"....Why, the DC-X was a technological demonstrator. A cheap one at that. ..." Actually the DC-X was a 'concept demonstrator' for rapid prototyping and flgiht operation. It was not a 'technology demonstrator' as majority of components were existing taken from Saturn and/or other programs. It demonstrated how a simple mission operation can be done without advanced technologies and a standing army of hundreds or thousands engineers and technicians. Somehow, when it comes to DC-XA funded under NASA, the tone changed. Everybody touted it as a 'technology demonstrator' as NASA is in love with new technologies but placed very little value on operations. This was when MDA was directed to work with the Russians on Al-Li tank, and putting different 'technologies' into the DC-XA. <div class="Discussion_UserSignature"> </div>

nacnud · Jul 28, 2005

Good correction, I think that makes all the difference.

seaborn · Jul 28, 2005

"15-20 years of service has obviously taken it's toll on the shuttle fleet. It was a good idea in the 1970s, however, the system is just not reliable anymore. NASA knows this." In my opinion I believe that the shuttle is no more or less reliable than it ever was. With the Columbia accident it brought forth the problem of debris from the external tank. From what I have read, the external tank has always shed pieces of foam. Its like anything else, it takes a disaster to bring the problem into the public eye. Examination of the TPS from past missions has shown that the vehicle has returned safely with damaged tiles. With that said I do believe it is time for a new program.

hurricane4911 · Jul 28, 2005

Your response to no_way illustrated my point.

larper · Jul 28, 2005

And I will always counter that there is a payload penalty associated with ALL landing systems, and so it is no penalty at all. The real comparison is in the weigth, performance, safety, cost, and reliability in each system. There is no evidence that a DC-X type landing system is any worse than any other in these respects. It really currently boils down to the assumptions that are made. If those assumptions are wrong, you end up with bad designs no matter how good the engineering is. There are seveal HUGE advantages to a DC-X type system that perhaps outweigh other assumed disadvantages, advantages that were actually demonstrated on the DC-X. As far as X-33 was concerned, the Lockheed concept was the absolute worst, in my opinion. And I FORMED that opinion while working for Lockheed Martin. No one can say that the other options would have gone further or not than the X-33 did. It is my opinion that the DC-Y would have flown successfully. It is other peoples opinion that it wouldn't. Until we actually try to build one, we will never know. <div class="Discussion_UserSignature"> Vote Libertarian </div>

no_way · Jul 28, 2005

<blockquote>In reply to:<hr />by using wings or parachutes you can use the atmosphere to reduce the vehicle’s velocity for landing<hr /></blockquote> Just because you can use it, doesnt mean you should. Wings on space vehicles, especially on vehicles reentering from orbit have their own problems as we are all well aware. And parachutes are a major problem for fast turnaround and thus also low operations costs. It makes sense to sacrifice some payload to immensely gain in operability and thus also save costs. I know that the usual aerospace crowd has traditionally favored performance over everything, but this is not a wise approach if you want affordable space flight. TheSpacereview.com is running a long series of interview with TVG Rockets people, there are lots of expanations in there why exactly they chose to go with VTVL. Armadillo Aerospace initally planned to do landing and recovery with parachutes. Well, they dropped the idea for two reasons : worst case failure modes caused lots of problems with liability ( i.e. if you accidentally deploy your parachute too high, you never know where you are gonna land ) and second, the turnaround time was just too much. Its obviously not a clear-cut case that VTVL is good and everything else is bad. But there are lots of arguments why VTVL could be favored over other launch/landing methods that could eventually lead to low-cost space transport. We'll wait and see. My prediction still stands, someone will build an affordable orbital space transport using the general principle of VTVL, probably two-stage design in not too distant future. We'll also see precursor single-stage suborbitals before that.

radarredux · Jul 28, 2005

> landing a DCX type vehicle on the Earth is not a good design because by using wings or parachutes you can use the atmosphere to reduce the vehicle’s velocity for landing. Carrying the engines and propellant to do a retro burn to land on a planet with a thick atmosphere is almost as bad an idea as jet engines on the Shuttle Orbiter./i> TGV Rockets (Two Guys and a Van (TGV)) uses a flexible aero-shield to slow it down. http://www.tgv-rockets.com/

larper · Jul 28, 2005

<blockquote>In reply to:<hr />Do the trade of retro rockets vs parachutes ! <hr /></blockquote> Parachute, N kilos. Landing rockets, 0 kilos. They are the same as the primaries. <div class="Discussion_UserSignature"> Vote Libertarian </div>

radarredux · Jul 28, 2005

>> "There are seveal HUGE advantages to a DC-X type system" /> And these hugh advantages are........../i> I think a lot depends on your goals. TGV wants to minimize costs to an extreme level for suborbital flights, so they don't want to do things like hire people and a crane or take a recently landed rocket and put it vertical for the next launch. As another example, Rutan has an winged approach for their suborbital missions (SS2), but they are looking at a capsule approach for their (t/Space's) orbital missions (CXV).

larper · Jul 28, 2005

The number one big advantage of a DC-X type system is full vehicle recovery after abort. DC-X actually demonstrated this inadvertantly when it had on on board explosion shortly after liftoff. NO, repeat, NO system ever existing or proposed had this capability. <div class="Discussion_UserSignature"> Vote Libertarian </div>

nacnud · Jul 28, 2005

The number one big advantage of a DC-X type system is full vehicle recovery after abort. £$^&# just think of the insurance saving on com sat launches!

larper · Jul 28, 2005

Well, to be fair, most satellites are lost due to booster malfunction or satellite malfunction, not launch vehicle malfunction. <div class="Discussion_UserSignature"> Vote Libertarian </div>

tap_sa · Jul 28, 2005

">> Do the trade of retro rockets vs parachutes ! Parachute, N kilos. Landing rockets, 0 kilos. They are the same as the primaries. " Fuel for landing rockets, Y kilos. Y depends on vehicle landing mass, how much velocity it has to shave off and how many seconds we want to be able to hover ie. fight against gravitational loss. I dont have exact idea how fast something like DC-X would descent but if we assume 400km/h final speed before retrofire and 30 seconds time to decelerate and land, you need 12.5% propellant (for example empty weight 10t, needs 1.25t propellant). And this assuming 350s specific impulse. 12.5% sounds like quite a lot ... but of course it being just propellant would simplify the design. Better be some extraordinary reliable engines!

larper · Jul 28, 2005

<blockquote>In reply to:<hr />12.5% sounds like quite a lot ... but of course it being just propellant would simplify the design. Better be some extraordinary reliable engines! <hr /></blockquote> Right. Ok, so now you have some figures. Compare against any other landing system. First, any other landing system is going to weigh something. Next., any other landing system is a different system than the launch system, so you have double the maintenance. Third, any other landing system is not tested during launch. The DC-X type is. If you detect a problem at launch that might effect landing, you can abort. You might have to do an abort that loses the vehicle, but you still save the crew. Any system has trade-offs. It is all in the assumptions being made up front. One of the assumptions with the shuttle was that, somehow, HL was safer and cheaper than VL. It turns out not to be case, and the whole design of the vehicle was dictated by that assumption. Build a DC-X type system. Fly it. Test it. See what assumptions were made that were wrong. Don't just say it won't work. That is what X33 should have been, a fly off of all possible systems, not the selection of a set of powerpoint presentations. DC-X flew. It worked. Build from there and see where it goes. If the assumptions made don't pan out to be true, then you move on. You don't build an entire system a la shuttle before you find out your entire premise was wrong. <div class="Discussion_UserSignature"> Vote Libertarian </div>

nacnud · Jul 28, 2005

The Soyuz return capsule is 9% parachute and IIRC the X-38 was around 20-30% parafoil. Oh and the Genesis achived lithocapture at about 200mph which is about 320kph.

larper · Jul 28, 2005

Ok, so we have something to compare against. If 12.5% is close to what is needed in a DC-X type system, then we are in the same ballpark as a Soyuz. Now, what are the drawbacks of a parachute that might be mitigated by a powered VL? Maintainability? Reliability? Redundancy? Abort modes? etc. Fly it, test it, prove it. Challenge the assumptions. It is how we got to the moon.... Assumption: LOR is too dangerous. Wrong Assumption: You need seats in the LM. Wrong. How many other assumptions were made at the beginning of the Apollo program that had to be challenged in order for the program to be a success? Now, let's look at the assumptions that were made that absolutely dictated the design of the shuttle: 1) Horizontal landing is good. This means we need control surfaces that are usesless during launch but need to work at landing time 2) Reusability is good. This means the vehicle has to land with virtually all of the pieces that it launched with, including engines. This means that the engines have to be on the re-entry vehicle, which means that the orbiter has to be mounted to the side of the tank instead of the top, which means it is in the debris field of the tank. This also limits the physical size of the engines, which means the boosters have to be even bigger and more dangerous. Which means the tank has to be made beefier to handle all of the extra torque and side-loads. etc, etc, etc. Just those 2 assumptions dictated most of the shuttle design. It turns out the assumptions are wrong, and so we end up with a system that is dangerous, expensive, and incredibly inefficient. Throw those assumptions away. They have been proven false. Now, free from them, what kind of vehicle can you build? Of course, you have to make other assumptions, you always do. That is what you are testing for. It is what engineering is all about. <div class="Discussion_UserSignature"> Vote Libertarian </div>

propforce · Jul 28, 2005

<blockquote>In reply to:<hr />Fuel for landing rockets, Y kilos. Y depends on vehicle landing mass, how much velocity it has to shave off and how many seconds we want to be able to hover ie. fight against gravitational loss. I dont have exact idea how fast something like DC-X would descent but if we assume 400km/h final speed before retrofire and 30 seconds time to decelerate and land, you need 12.5% propellant (for example empty weight 10t, needs 1.25t propellant). And this assuming 350s specific impulse. 12.5% sounds like quite a lot ... but of course it being just propellant would simplify the design. Better be some extraordinary reliable engines! <hr /></blockquote> Pardon my lack of understanding, but how do you arrive the 12.5% of total (initial) propellant mass as the required landing mass, when you don't know what the landing weight of the vehicle is???? The other thing is that you'll need to trade the mass of landing propellant (and engines with gimbal actuation system, if separate from ascent engines) with wing, TPS under wings, landing gears, landing gear doors, TPS under the landing gear doors, the hydraulic actuation systems required for both wing flaps, rudder, and landing gears (too big for EMA). Trading off landing propellant with structures, propellant is always cheaper. Also trade the inherent reliability of moving parts with non-moving parts. In this case, it's the ability to start and gimbal the landing engines versus wing flaps, rudder, and landing gears. A non-wing vehicle sitting on top of a booster is also require less structural strength than a wing-vehicle, as a wing-vehicle needs to designed for the asymmetric aerodynamics loads into its structures. This either eats away additional structural margin, or the resultant vehicle has less propellant mass fraction and/or less payload capability. Finally, tere's nothing stopping a future VL such as DC-X like <div class="Discussion_UserSignature"> </div>

propforce · Jul 28, 2005

"...The Soyuz return capsule is 9% parachute ..." Does the Soyuz return capsule has retro-rocket as well ? <div class="Discussion_UserSignature"> </div>

mrmorris · Jul 28, 2005

"The Soyuz return capsule is 9% parachute and IIRC the X-38 was around 20-30% parafoil." Do you have links on those figures? This document indicates the X-38's parafoil alone weighed 9.8% of the landing weight as compared to the Apollo parachute's 2.8% of capsule weight. I can't find a link for the Soyuz parachute, but it's hard to imaging it being that much higher than the Apollo's.

tap_sa · Jul 28, 2005

"how do you arrive the 12.5% of total (initial) propellant mass as the required landing mass, when you don't know what the landing weight of the vehicle is?" Simple rocket equation calculation finding out what the required massratio is to achieve 30s * g + 400km/h deltaV when you have 350s specific impulse. The reality is of course much more complex as you pointed out in the rest of your post! But it was something to start with.

nacnud · Jul 28, 2005

I could well be mistaken but those figuers were on SDC in the last week or so.. Edit: OK I FUBARed, mrmorris you said: The X-38 parafoil was over 12% of the landing weight. By contrast, the Apollo parachute system was less than 3%. Parafoils are significantly more complicated, larger, and heavier than a parachute with an equivalent capacity. Oops sorry.

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