WHY haven't we mastered reusable rockets yet?

Question

it seems elon musk and the billionaires are in a battle to provide NASA with the first generation of re-usable rockets.

surely re-usable rockets will save money and by extension costs of getting to space.

after the success of the 1960s we shud have pooled resources into creating better reusable rocket technology for the next generation of astronauts in the 70s and 80s.
why didn't we do this? did we try to and fail or did was NASA misguided in its priorities?

Answer 1

Actually we did. In the early 1990s McDonnell-Douglass flew a prototype reusable rocket called Delta Clipper or DC-X demonstrating many of the same technologies that SpaceX is trying to achieve. DC-X in a number of flights successfully demonstrated rocket-borne hover, approach to landing and landing. In one test DC-X landed at its target landing area and then took off again and flew back to its starting point.



However, there is a reason why in 22 years since DC-X's first flight nobody made use of this technology. The reusable first stage does not come for free. The launch vehicle weight at lift off is much higher than it needs to be and the cost of building and operating a reusable launch vehicle are actually higher than that of an expendable one.



First, you need to reserve a lot of fuel for reentry, rocket-borne descent and landing. Second, the structure of the first stage will have to be much heavier than the expendable to take the stress of reentry and landing. It would have to incorporate some kind of landing gear to allow for soft landing.



Third, during a typical launch the main engines run for about 5 to 7 minutes. The reusable stage's engines will run for about 20 minutes. You need larger batteries and more hydraulic fluid to keep them running. Unlike aircraft, rockets use open hydraulic systems where hydraulic fluid is used once and not recycled. The engines of reusable first stage will also have to be capable of deep throttling to allow fine control during the final approach. This adds a great deal of complexity and cost to the engine.



Forth, as I mentioned earlier, a typical expendable engine runs for 5 to 7 minutes during launch. To ensure against failure the engineers design parts of the engine to operate up to 15 minutes. If you plan to run an engine for 15 minutes you have to design the parts to run at least 30 minutes. The only way to do that is make them heavier (and more expensive.) If you want to use the engine multiple times you have to make the parts heavier still.



You can argue that by using some exotic alloys the designers can minimize or even negate the weight penalty, but they could also make even lighter parts for the expendable engine out of the same materials. Anyway, these "exotic alloys" usually cost orders of magnitude more than the more conventional ones, so if you want to use them you incur a cost penalty.



All these things add to the lift off weight of the launch vehicle. Using a wholly expendable launch vehicle you can either use a much smaller and less expensive launch vehicle to lift the same payload or use a similarly sized vehicle to launch a heavier payload.



And finally, if I was a customer, I wouldn't want my satellite riding on top of a reused first stage if it hasn't been thoroughly overhauled and tested after its previous flight. This overhaul would involve a complete tear-down and reassembly the the engines and airframe. The most expensive part of the rocket is the engine. The biggest cost of the engine is the labor to put it together. The same highly paid craftsmen who built the engine will be the ones taking it apart and then putting it back together, completely negating any cost advantage of reusable engine.

Answer 2

We didn't do it because we didn't need to. Money and politics drives everything. Reusable rockets are only necessary, or even desirable, if you're doing a LOT of launches. There's no reason for that many launches unless you're supporting a large manned presence in space. Something politicians have never given two s***s about. The space race had less than nothing to do with exploration. It was a public way of demonstrating nuclear missile technology as a deterrent during the Cold War, without triggering a hot war. The space shuttle likewise had nothing to do with exploration. NASA didn't even want the shuttles, they wanted to continue with the Apollo Applications Program. Congress forced the shuttles on NASA, largely due to their ability to launch, and especially recover, military payloads. There were 135 shuttle missions, 7 of those remain classified to this day.

Answer 3

Rockets are hard things to control... And, we *did* have some examples - the space shuttle was reusable. There was talk of equiping a Saturn V 1st stage with parachutes & floats - but, it added weight and expense to an already expensive project, and would've required several test flights.

The X33 and the Delta Clipper projects were exactly that - a single-stage-to-orbit craft, 100% reusable; but, the added expense and brick wall of engine performance cancelled both of those.

While it's never been practiced, the *thought* of reusable rockets has alwas been there - now, the technology and circuitry is getting small enough and cheap enough to warrant it.

Answer 4

How far are you behind things? The space shuttle first launched in 1980 was both reusable and used reusable boosters . We have been there for a while . If you are talking about a single unit that with out dropping boosters can be reused , dream on. Boosters are used and dropped because it takes too much energy to put that much mass into space. We could do it but it would cost 500 to 1500 times as much to do it and it is not worthwhile.

Answer 5

"WHY haven't we mastered reusable rockets yet?"



Because we always launch over ocean, because we want to go into orbit or beyond.



"it seems elon musk and the billionaires are in a battle to provide NASA with the first generation of re-usable rockets."



Sure.



"surely re-usable rockets will save money and by extension costs of getting to space."



Nope. Makes no sense to try and soft-land, on ocean. That is where the first stage is, unless you launch eastward, from California. So any mistakes, land on US citizens. Not saying we don't deserve some flak, but...



"after the success of the 1960s we shud have pooled resources into creating better reusable rocket technology for the next generation of astronauts in the 70s and 80s."



We had serious problems getting reusable engines. Finally figured out in the Space Shuttle... about a decade late.



"why didn't we do this? did we try to and fail or did was NASA misguided in its priorities?"



We want stuff that cannot kill people, for ordinary launches. Which means the first stage not only soft lands, but has to fly to a destination.



(I apologize in advance for the "Americanese" that follows.) So, we'd have to launch over the Atlantic, and soft-land in Africa. Either ship it back, or launch from Africa and land in Antarctica (which has no facilities yet), which gives us a chance for a polar orbit, but little else. Or launch from Africa back towards the USA for a shorter lived orbit. I just don't see it, without flight capabilities. Sort of along the lines of the Space Shuttle on the back of a 747, only with a faster 747.

Answer 6

The concept of reusable rocket technology has been around ever since the rocket itself was first conceived. In fact, the earliest designs probably started off with such intentions. Examples of rockets that can launch and land at will are even the preferred method of travel in popular science fiction works dating as far back as the 1950's.



The complications that had prevented engineers from further developing the concept was in construction materials. The strength, stiffness, heat resistance and low weight characteristics of the available construction materials of the time were insufficient to withstand the rigors of repeated exposure to the extreme environments associated with launches, low-Earth orbits and re-entries.



During the 70's and early 80's advances in metallurgy started to catch up with the concept of reusable rocketry. The first practical application of reusable technology came in the form of the multi-stage NEXUS launcher by Krafft Arnold Ehricke. An engineer by the name of Philip Bono is considered a pioneer in the industry. He had proposed several launch vehicles including: ROOST, ROMBUS, Ithacus, Pegasus and SASSTO.



In short, Elon Musk and the SpaceX Corporation are far from the first to design and develop reusable technologies. He is simply carrying on within a long line of engineering innovation and design that dates back to the dawn of the rocket age itself.

Answer 7

As both the billionaires have discovered, getting a rocket to come down vertically and to an exact stop at the Earth's surface isn't easy.

Other attempts at reusable (including the Space Shuttle) have looked at wings, which add a lot to the launch weight. It has been cheaper to make the tanks as light weight as possible and throw them away.

Answer 8

Chemical rockets are very marginal in engineering terms. The energy you get from burning liquid oxygen and liquid hydrogen to water is only very slightly more than the energy needed to put that water molecule into orbit. So the whole thing is marginal, requiring multiple stages that are thrown away, etc. The space shuttle did a fairly good job of it, given the materials and fuels we have.

Answer 9

because the rockets we have work just fine.



a reusable rocket would have to work a *lot* better (economically, technically, whatever) to be viable. working a little bit better isn't good enough.

Answer 10

Because it's cheaper to build a new one than try to rehab a used one.