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Why aren't more parts of spacecraft commonly reusable?

As I'm looking at the Soyuz plans, the three parts don't seem all that different in terms of survivalibility. The orbital module resembles Voskhod which was meant for reentry. The Service module seems quite similar in shape to the Descent module. I understand the fragile solar panels wouldn't withstand the reentry, nor would most of external parts, but wouldn't a coating of ablator and a parachute allow to recover most of the systems for refurbishing, even with the structural elements bent out of shape and burned?

What is the hardest part of making a module (partially) reusable? What's so expensive that letting it burn in the atmosphere is cheaper?

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    $\begingroup$ Maybe because costs for design and testing dominate over manufacturing costs, and the launch frequency has been so low due to complex operations and low demand, that it hasn't been worthwhile the hassle and increased design costs. Relatively high risk of failure could also have been an argument against reusability. 1.5% launch failures meant that 25% of the Space Shuttle fleet was destroyed each time. $\endgroup$
    – LocalFluff
    Nov 13, 2015 at 13:39
  • $\begingroup$ @LocalFluff: I failed to understand "1.5% launch failures meant that 25% of the Space Shuttle fleet was destroyed each time". Would you please elaborate? $\endgroup$
    – Emilio M Bumachar
    Nov 13, 2015 at 15:32
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    $\begingroup$ @EmilioMBumachar 2 out of 133 Shuttle missions failed. At each time there were 4 shuttles. A new one was built after the first failure and turned the 3 into 4 again. Point is that the overall future capacity of the entire operation is much reduced by each failure for reusables, but not affected by the loss of expendables. A shuttle made on average more than 25 launches, one lost means up to 25 lost launches. The launch might be cheaper, but not necessarily the vehicle. $\endgroup$
    – LocalFluff
    Nov 13, 2015 at 15:36
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    $\begingroup$ @LocalFluff: The Shuttles are really a poor example though, as instead of money-saving, their recoverability was a money drain. Enormous amount of dead weight made the launch costs to balloon, and the complexity necessitated extremely complex safety tests. Payloads to orbit should really travel in a fairing and not in a cargo bay. $\endgroup$
    – SF.
    Nov 13, 2015 at 15:44
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    $\begingroup$ @LocalFluff: It means an enormous fuel tank and two huge SRBs. Fuel, size, mechanical complexity (durability), payload fraction, kilogram per dollar. Lifting the huge cargo bay, the big wings, their respective heat shielding - that all cost a fortune both in money and in fuel, in construction of tank to hold that fuel and in construction (and more dead weight!) of the whole thing to hold a tank this massive. $\endgroup$
    – SF.
    Nov 13, 2015 at 15:56

4 Answers 4

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The hardest part of making a spacecraft reusable is making it cheaper to re-use than to let it burn up. Every gram you add in weight makes launch more expensive, and a spacecraft that can be re-used is going to be considerably heavier than a disposable one.

In addition to launch costs you have to factor in the costs of refurbishing and re-certifying a spacecraft after its been through the rigors of launch, space travel, re-entry and recovery. You can't just take the spacecraft, brush it off, re-fill it with hydrazine and stick it back up on top of a rocket, you have to test and repair all the systems on board. The shuttle program showed that these costs can be higher than outright replacement of the spacecraft every time.

Note that the newer spacecraft designs are for re-usable spacecraft, using lessons learned from the STS program and new technologies and materials to make it costs effective.

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  • $\begingroup$ But how does mass of the rocket in itself enter the equation, if it is reusable? Fuel cost is less than 2% or so today. Falcon9 v1.1, which is the version SpaceX actually has tried to land, is 50% heavier than v1.0 on the launch pad. What does that matter if its reusability succeeds? Mass to orbit is something else than mass back to Earth. Reusable mass is almost irrelevant compared to the mass of expended equipment. $\endgroup$
    – LocalFluff
    Nov 13, 2015 at 14:26
  • $\begingroup$ That all seems a contradictory @LocalFluff, I'm having trouble parsing it. $\endgroup$
    – GdD
    Nov 13, 2015 at 15:18
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    $\begingroup$ A more massive spacecraft is going to mean a bigger rocket or less payload for the same orbit, so it's a cost. Also, you could buy a used Cessna for way less than chartering a jet, trust me I'm a pilot ;) $\endgroup$
    – GdD
    Nov 13, 2015 at 15:29
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    $\begingroup$ That's only if the rocket is re-usable, the question is about making a reusable spacecraft. $\endgroup$
    – GdD
    Nov 13, 2015 at 15:31
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    $\begingroup$ @LocalFluff: Economy of scale. You could buy a lifetime of Cessnas to parachute out of and dispose of after each flight for the cost of one JumboJet and the airport to support it. Now imagine your Jumbo Jet can only take four passengers and maybe 2 tons of payload. You'd be still better off with the disposable Cessnas. $\endgroup$
    – SF.
    Nov 13, 2015 at 16:12
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Recovering the physical material is easy enough, but making it fly again is harder.

The price of a space craft failing is spectacular. This is doubly true for manned missions. The required reliability of parts scales in kind. Its much easier to develop highly reliable parts to work once than it is to make parts that achieve the same reliability time after time after time. There's a lot of inelastic deformations and irreversible changes which occur in hardware in flight, especially when you play with ideas like a parachute assisted landing! Building to make these elastic and reversable increases weight and increases cost. You also have to build them to be re-inspectable, which is not always easy.

In general, challenging weight or shape requirements create highly customized solutions. A closer to home example is the cellphone market. Batteries used to be replaceable, so when one got used up (from too many launches.. I mean phone calls), you could swap it out. Now days, as phones have gotten thinner and battery demands have gotten higher, you see batteries glued into the case. This is abysmal for the replacement battery business, but it shaves off a fraction of a millimeter from the phone dimensions!

Now a cell phone is a commodity device. Expand that effect correspondingly for a vehicle that has to hurtle into space, with a small market.

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I suspect it's mostly a problem of weight vs. drag. If you wanted to land all 3 modules of a Soyuz, you'd have 3 times the weight of the descent module, but the heat shield area would remain the same. So the ballistic coefficient would drop and your speed during reentry would be higher. This means you need a heavier heat shield.
You also need larger parachutes to land the increased mass. The extra mass of parachutes and heat shield has to be launched etc. and you have a weight spiral on your hands.

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  • $\begingroup$ In this particular case I imagined Soyuz still splitting into three parts before reentry; unmanned modules can withstand much higher acceleration, heat and impact than human bodies so less "thorough" survival features would be needed. The reentry module would reenter just the same as it normally does. The other two modules would have no spare parachutes, no landing engines, possibly smaller parachutes, less thorough heat shielding. They might even have some "crumple zones" destroyed upon impact, but the most expensive and complex systems - electronics, engines - would be recoverable, $\endgroup$
    – SF.
    Nov 13, 2015 at 14:40
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    $\begingroup$ That still at least doubles, if not triples, the mass budget for re-entry specific systems. The Soyuz reentry capsule is the smallest part of the ship, but masses more than twice the orbital module, and about the same as the service/propulsion module. Total Soyuz spacecraft mass is about 7 tons; you'd add another ton and a half or so. $\endgroup$
    – Russell Borogove
    Nov 13, 2015 at 18:03
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There was a similar question earlier today regarding rockets. Basically in space systems risk aversion is a very big thing, so there is a tendency to reuse systems that have been proven to work, so there is reusability in that sense.

The real reason though is that there is no incentive for companies to design such systems. Those are government funded contracts, they tend to be cost plus (cost plus guaranteed profit), so you end up with custom built one off vehicles.

The space shuttle was reusable but only after extensive rebuild after each flight.

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