Solid Vs. Liquid Rockets Options

[Chmee]

I am no rocket scientist, but it seems to me that the cheapest way to space for unmanned missions would be to use rockets with solid fuel and not liquid. Solid rockets are much, much simpler than liquid rockets since they have virtually no moving parts (no pumps, engines, etc). It has been my experience that the simpler the design, the fewer potential points, and thus opportunities, for failure.

This simplicity also translates into a much easier assembly process, and thus lower cost. So why don't we use some modified Shuttle SRB's to get into orbit?

I know that that solid rockets have some "drawbacks", in that they cannot be throttled nor turned off once lit. But how many (unmanned) launches have we seen that needed the thrust to be cut? If the rocket went off course, they are blown up immediately, regardless what kind of fuel is in them.

I believe that solid fuel is not as efficient as liquid (at least does not have a high ISP). However, if it is 4 times cheaper to assemble a solid rocket vs. a liquid, the higher fuel requirement should not be a big deal; just make the rocket a bit larger and it will still be much cheaper.

Are there other issues that I did not list that would make using solids not desirable? If there are no other issues, why isn't the space industry using them now for cheap access?

[Bob Shaw]

Using SRB-derived rockets for manned launches has been given serious support by the new NASA Administrator, who says also that he already has a heavy-lift vehicle available - the Shuttle stack without the Orbiter.

These are persuasive concepts, though the new Hybrid rocket motors (as used by SpaceShipOne) have some very attractive features, being non-toxic, non cryogenic, and able to be throttled - albeit with a poorer specific impulse than Hydrogen/Oxygen etc.

I can't honestly see unbuilt and expensive Titan-IV class boosters competing, somehow - the post-Shuttle landscape will surely use as much Shuttle hardware as possible, and thereby will save zillions on the launch support side of things...

[edstrick]

Big solids burn very very very rough.... the Shuttle astronauts <AND THE SHUTTLE> are shaken so violently during the solid burn that the astronauts can't hardly even see the control panels. It's like being strapped inside a can on a paint-can-shaker. Once the solids are jettisoned, the ride is "like glass", I think somebody said.

Solids can DETONATE... as on at least two Titan 3/Titan 4 launches, a Delta's solid booster, others I know of but don't have ID's on. I'm still surprised Challenger's solid didn't as it burned through.

What we need is reusability. ...but... without a standing army of tech's needed to do the reusability. The Shuttle was supposed to be reusable. It's not. It's refurbishable. Same for the solids, but they do have significant cost savings compared with flying throwaway solids.

We have to face the fact that THE SPACE SHUTTLE IS A FAILURE.
It was supposed to 1.) Provide access for crew and cargo to and from space and serve as a workplatform in orbit. It does that fairly well.

But it was also supposed and required to 2.) do it frequently ... 50 times per year when they were proposing the shuttle .... 3.) do it cheaply ... $50 million per flight, $20 of the the cost of the flight, $30 of that program cost. <granted.. 1971 dollars> .... and 4.) they were supposed to fly thousands of times safer than expendible boosters.

The shuttle fails #2 by 10x, #3 by 10-20x, and #4 by 100 to 1000x
Failing one of the four makes the "SPACE TRANSPORTATION SYSTEM" (what happened to the rest of the system?....) a failure. Failing 3 of the 4 makes it a 30 year catastrophy for the space program.

[Chmee]

Well, not to go too off-topic but...

I agree with you that the shuttle has not lived nearly up to its promise, however, it is not so much a cost issue as it is a re-useability turnaround issue.

Most of the cost of the STS program is in fixed costs (mostly salaries) that has to be paid regardless of how many flights are done per year. The more flights, the more of these fixed costs are spread out. If you assume the shuttle program costs about $5 Billion per year (as it currently does, flight or no flight) and we have 50 flights, then it is $100 million per flight. Adjusting for inflation, it is in the ballpark of the $50 million in 1971 dollars you quoted.

So it wasn't the total cost that NASA got wrong, it was how many times they could (safely) turn the shuttle around per year. As you correctly pointed out, it is more a refurbishment rather than reusable vehicle, because of its immense complexity.

Nasa also ridiculously assumed 50 flights per year, which would be the entire world demand for launches *today*, and way more than was needed in the 1970s/ 80s.

Having said that, while this shuttle fleet has not lived up to all the promises, I beleive that the shuttle concept is still valid and this will not be the last time this system is used (though it might be in our lifetimes).

A much simplier, re-usable, smaller shuttle may someday fulfill this promise.

[dvandorn]

... it wasn't the total cost that NASA got wrong, it was how many times they could (safely) turn the shuttle around per year.  As you correctly pointed out, it is more a refurbishment rather than reusable vehicle, because of its immense complexity.

Nasa also ridiculously assumed 50 flights per year, which would  be the entire world demand for launches *today*, and way more than was needed in the 1970s/ 80s.

Originally, the 50 flights per year rate was based on 10 flights per year for each vehicle in a 5-orbiter fleet. The idea was that they would turn around each shuttle in about four weeks. When I saw exactly how much tear-down and rebuilding had to be done after each flight, I knew they would never, ever approach that launch rate.

And because they would never even get close to that rate, they couldn't bring the per-flight cost down to where launch costs per pound would have encouraged more and more launches. I don't think the concept that "lower per-pound launch costs will result in more business for space launches" is totally invalid -- in other words, bring the costs down and you'll have more payloads.

The *real* problem is that you'll never generate a need for a high flight rate until you bring the costs down, and no one will spend the money to develop a system that can be rapidly turned around and re-used because you can't demonstrate that there is a need for it. It's a vicious circle.

It also doesn't help that most of the companies capable of building such a launch vehicle have *zero* interest in bringing down launch costs. They're making huge profits by building three or four billion-plus-dollar throwaway rockets per year. They don't want demand to increase -- as long as they keep the launch costs high, they make more money. So they don't even make a decent try at it...

-the other Doug

[The Messenger]

Originally, the 50 flights per year rate was based on 10 flights per year for each vehicle in a 5-orbiter fleet.  The idea was that they would turn around each shuttle in about four weeks.  When I saw exactly how much tear-down and rebuilding had to be done after each flight, I knew they would never, ever approach that launch rate.
snip

It was also based upon supporting commerical satellite launches, which Reagan nixed after the first shuttle failure. The idea was to spawn a vibrant US commercial rocket business, but most of the satellite launch business just moved to other countries.

The current 'next-generation' manned-space replacement concept is to use one Shuttle derive solid rocket booster, and an expendable second-stage derived from Apollo boosters, which are less complex than the space shuttle main engines. The 'crew vehicle' would also be capsule-like, but never identified as such.

For heavy-lift, the design is to use two five-segment shuttle boosters for the first stage and an Apollo derived second stage. (The current shuttle uses four segment boosters.)

This was THE plan after the shuttle is retired in 2010, before the latest foam fiasco, so everything is under review, but I don't see any strong reasons, political or otherwise, for Griffin to change direction.

[edstrick]

The fundamental fact is that the shuttle is a failure, and it's taken vast amounts of money and two catastrophies to beat it into a bunch of rocket-BUREAUCRAT'S and politician's heads.

The shuttle was supposed to 1.) put payloads and crew in orbit and return them, and serve as a work platform in orbit. It does that fairly well. I'd guesstimate 80% of goal.

But. Shuttle was supposed to fly 2.) frequently: 50 times a year for the fleet of 5... we can't fly 5 times a year. 10x failure.

Shuttle was supposed to fly cheaply: $20 million recurring cost per flight, $50 million amortized over the entire program. After 3x inflation since 1971, that's $150 million. Real cost per flight, including development and costs whether we're flying or not... maybe $1.5 billion... 10x failure.

And Shuttle was supposed to fly safely. Tens or hundreds or thousands of times more reliably than expendible boosters. Take your pick of the versions of that propaganda through time. I don't recall the number when they were proposing the shuttle.... They fail maybe 100x.

On any of thouse 10x or 100x counts, the shuttle is a failure... with 3 out of 4 essential goals blown. ... (sigh)

THIS SHOULD NOT BE AN ARGUEMENT THAT THE IDEA OF A SHUTTLE IS BAD. As the fox said (according to Aesop), when he couldn't reach a bunch of grapes: "They're probably sour anyway".

[djellison]

It does everything it was designed to do, just too infrequently and too expensively.

Doug

[abalone]

Well, not to go too off-topic but...
So it wasn't the total cost that NASA got wrong, it was how many times they could (safely) turn the shuttle around per year.  As you correctly pointed out, it is more a refurbishment rather than reusable vehicle, because of its immense complexity.

If that is not a cost issue I dont know what you would call it. They can't launch more missions because it takes 10X as many resources to turn the thing around between mission than what was envisaged

[abalone]

It does everything it was designed to do, just too infrequently and too expensively.

Doug

And too deadly!!

The concept of launching cargo and crew in one large complex craft has turned out to be an error of judgment. The cost of supplying the same margin of safety for cargo as for crew is the weak link in the shuttle. Cargo should be launched on cheap expendable rockets and docked to the crew module in space. This is something the Russians have been doing for years and who is the only country in the world with an operational manned space program for the last 2 years and next? years.

On the point of all solid booster I can only point to the market and say the cheapest most realiable systems are now the market leaders. All are liquid with solid boost at launch. The specific impusle is simply too small and they can only deliver 25% of the orbit weight of a liquid, ie. they would need to be 4X as big, therefore 10X? cost

Even if all the other drawbacks of solids could be overcome the need to be able to throttle is indispensible. Basic physics dictated that thrust needed to lift the craft off the pad has to be large, solids are good for this. As mass is lost, acceleation increases and would rapidly surpass that which a crew could handle if no throttle is available. The unmanned launch vehicles currently in use would kill the crew for this reason unless they were modified. It is also less fuel efficient to send cargo with crew for this reason. Crewed launches are what? 3.5G max, uncrewed 7G. Remenber that the fuel needed to achieve 1G is all wasted as if simply overcomes gravity, every extra second that the launch takes wastes fuel in this way.

http://en.wikipedia.org/wiki/Rocket_fuel#Solid_propellants

[The Messenger]

I couldn't agree with you more, with minor clarifications.

Solids can be configured to throttle back - the Space Shuttle boosters launch at full power, then the thrust is reduced ~30 seconds into flight (to minimize low atmospheric drag) then increase in thrust again in the upper atmosphere. This is accomplished by designing variations in the propellant grain surface area.

The solids get the shuttle of the ground in a hurry - giant nozzles, which reduces the energy wasted fighting gravity. If you watch the Apollo launches - it took more than three times as long to clear the launch pad as the Shuttle. So the rough ride has a trade-off.

Solid propellants have lower specific impulse, but are much more dense, packing more than twice the energy in the same volume as liquid H2 and O2.

One final comment: Both solids and liquids have catastrophic failure modes, but solids are more difficult to inspect for cracks and other propellant flaws that will not be obvious until the match is lit. So the safety margins have to be maintained by carefully controlling the manufacturing process, and understanding the aging process of the propellant and supporting hardware.

[abalone]

The solids get the shuttle of the ground in a hurry - giant nozzles, which reduces the energy wasted fighting gravity. If you watch the Apollo launches - it took more than three times as long to clear the launch pad as the Shuttle.  So the rough ride has a trade-off.

It is my undestanding that acceleration was higher for the Apollo's overall

[djellison]

I've read 15 minutes for a Saturn V launch. Give than a Shuttle launch is less than 9 minutes, the average acceleration would be lower for Saturn V, but there may be peaks that are higher than the Shuttle

Doug

[dvandorn]

The Saturn V required between 11.5 and 12 minutes to place the TLI stage (full Apollo CSM/LM, SLA, S-IVB and remaining fuel) into a low earth orbit (about 150 km high). The shuttle places a somewhat lighter total payload into a somewhat higher orbit after roughly nine minutes.

Recall, too, that the Saturn V used higher-density RP-1 and not liquid hydrogen in its first stage -- this provided the necessary lift-off thrust to get the whole thing off the ground. While the Saturn's upper stages, which used hydrogen and oxygen, were more efficient than the first stage, they couildn't deliver the kind of massive lift-off thrust required of the first stage.

-the other Doug