7
$\begingroup$

If SpaceX starts reusing boosters, it has to be assumed there is an increased risk of catastrophic failure until proved otherwise. If my payload was going to be on top of one of those boosters, some extra safety measures would be very reassuring. How about equipping the final stage bearing the payload with the kind of abort system the new Dragon capsules will have?

How much would the payload fairing need to be re-engineered and how much of a hit would the payload capacity take? Since they would be saving on the booster, couldn't the expense be worth it?

Improve this question
$\endgroup$
2

2 Answers 2

Reset to default
7
$\begingroup$

it has to be assumed there is an increased risk of catastrophic failure until proved otherwise

I contest this point. What SpaceX is attempting to do is tranform the rocketry model into something more equivalent to the airline model. Various components on aircraft are rated for so many hours of flying, and are inspected at regular intervals. Although rocketry definitely pushes the limits of material science further than aircraft do, I see no reason why it shouldn't be possible to rate certain componentry on a rocket for a number of flights.

It might end up being that a slightly used rocket ends up being more reliable than a brand new, untested one. There's no indication your statement is true.

Onto your actual question. It's simply not worth it - both in terms of cost and performance.

The Falcon fairing is made of Aluminium Honeycomb attached to a carbon fiber laminate with cork. It weighs a few hundred kilograms. The reason it is so light is to maximize the total payload that can be carried to orbit. It would take major structural modifications for the fairing to handle the g-forces associated with a SuperDraco abort scenario (up to 8G, I believe). This would add many tonnes of weight (not to mention complexity and propellant) to the vehicle, and would significantly reduce the marketable payload.

Going even further, if you were to face a late inflight abort (at stage separation, the Falcon 9 first stage is already traveling at approximately 1.8-2.0km/s, and needs to conduct a reentry burn for it to survive), you'd need heatshielding and protection built in. Which adds further mass.

Additionally, it is unlikely that the satellite would be able to handle the stresses associated with a complicated abort scenario. Some satellites are already built such that they can only handle stresses vertically, and require vertical integration on the pad (this is one of the many reasons the USAF is requiring Falcon 9 be stacked vertically for military and reconnaissance flights). If a satellite can't even handle being horizontal, it's unlikely it could handle the G's pulled in an abort.

A far better model, and the one that SpaceX is pursuing, is to simply make the vehicle so reliable you need not worry about failure. That's SpaceX in a nutshell, really: Keep It Simple Stupid.

Improve this answer
$\endgroup$
9
  • $\begingroup$ As far as reliability, please focus on the 'until proved otherwise' part. That proving definitely has to happen. It will also take quite a while. Until there are multiple stages around that have each been used 20 times, the case can't be made that they are just as safe, never mind safer. $\endgroup$
    – kim holder
    Nov 13, 2014 at 21:57
  • 1
    $\begingroup$ @briligg. True, but that's why I phrased my comment in the present tense. They're attempting to do so now. They have already fired single engines dozens of times, even hundreds of times at McGregor, so they do have a good understanding of how the engines (a.k.a. 80% of the componentry of the first stage) hold up over time. Proving the fuselage and tankage are okay for repeated launch cycles will take time. $\endgroup$
    – marked-down
    Nov 13, 2014 at 22:00
  • $\begingroup$ Fair enough. Excellent detail on the fairing structure, by the way. I'd accept it as the official answer, but i think i should give it more time. $\endgroup$
    – kim holder
    Nov 13, 2014 at 22:03
  • 1
    $\begingroup$ @briligg. No problems - let me know if you think I could expand/improve my answer in areas. I could provide more detail on the fairing but I'm sort of obliged to hold my tongue. $\endgroup$
    – marked-down
    Nov 13, 2014 at 22:05
  • $\begingroup$ @Briligg "That proving definitely has to happen." Don't stick cargo you can't afford to lose on the first few reused stages? A complex emergency system would also need testing - so all you're doing is moving risk and likely increasing it. $\endgroup$
    – NPSF3000
    Nov 14, 2014 at 1:33
4
$\begingroup$

There has been little publically said by SpaceX on this topic, but it would make sense to eventually phase out Dragon V1 (Current Dragon) in favour of the basic Dragon V2 design. Musk has said that they will stay with current cargo version for the near future. But that really just seems like it finishes out the CRS-1 contract. CRS-2 is being negotiated/bid now.

After all, why maintain two different product lines, when you can consolidate down to one? The main difference that will need to remain (maybe) is the docking port. Current cargo uses a CBM port which is bigger/wider than the NDS/LIDS/IDS standard that cargo will have to use. Of course CRS-2 makes it clear that using the PMA/LIDS/IDS/NDS dock vs berth is an acceptable possible option.

Improve this answer
$\endgroup$

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge that you have read and understand our privacy policy and code of conduct.

Not the answer you're looking for? Browse other questions tagged or ask your own question.