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Comment by matheusmoreira | Hacker News Reader

Before I learned about SpaceX, I thought it was literally impossible to reuse rockets because they burned up in the atmosphere or something. After all, not a single space agency in the world was doing it. Surely the smart engineers working in those places had good reasons.

Watching SpaceX land rocket boosters on target again and again is kind of magical, like something out of Kerbal Space Program. I wonder how long it's gonna take to get a fully reusable rocket. They're working on the Starship and it's supposed to be fully reusable.

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You need economy of scale for reuse to makes sense. Space launch market still isn’t that big, and even for spacex half of their launches are from their internal project, starlink. Jury is still out if this is actually economical, as we don’t have insights into their financials and they keep on raising money (so we don’t know if some portion of that goes towards flacon subsidies).

There is no doubt that a reusable rocket will be more economical. You need cheap rockets first to get economies of scale. It's gonna be big in the future.

The only thing that burned up in the atmosphere for the Space Shuttle program was the fuel tank. All the other components, including the booster rockets, were recovered and refurbished for reuse.

The innovation here isn't about reusability at all, it's about the economics of reuse. Maybe landing a rocket back on the pad rather than recovering them from the ocean makes it cheaper to reuse, has there been a study around that?

Yeah, SpaceX’s reuse is much, much simpler than the shuttle booster refurbishment. At the extreme, Starship is intended to have no refurbishment between flights - refuel and fly again, so that the cost of each flight will be mostly the fuel cost, on the order of single digit millions. Falcon 9 I believe is trickier since its kerosene fuel generates a lot of soot compared to the methane engines of Starship, and can be fouled. If you’ve ever used a camp stove with kerosene vs methane, one leaves your stove covered in black soot.

>Starship is intended to have no refurbishment between flights - refuel and fly again

Surely this entails a host of quality checks between flights? What is that cost estimate at?

This is based on pretty old info, which probably comes from an offhand statement by Musk, so big grain of salt, but I think they’re hoping to get it to be on par with a jetliner, which if I understand correctly is just a maintenance schedule based on # of flight hours. Not sure if that’s going to be feasible given the difference in the violence of the flight profile.

That would be interesting to hear how they come up with those maintenance schedules. Even with the uptick in flights, it doesn't seem like they'd have the dearth of reliability data to make that determination with reasonable accuracy. But maybe they have a lot of internal reliability data we're not privy to.

The reliability data will be collected by inspections. Also from memory, their fleet leaders tended to do Starlink launches. Loosing one of those might suck, but can still be sold as due to pushing boundaries and something that wont happen to customers. They need backup launch equipment, ofc.

The gold standard for reliability studies involves collecting in situ failures though. You can infer a lot from inspections on non-failed components, but it's not as useful as having actual failure data. When I'm referencing their in-house data, I'm referring to failures (whether in situ or as a bench experiment)

Just FYI, "dearth" means scarcity. Perhaps you meant wealth.

Thank you.

Note that for the Space Shuttle, the external tank was large proportion of the fuel-carrying capacity of the vehicle, i.e. "most of the rocket". And for the solid rocket boosters they were not fully recovered as they ejected the rocket engine bell just before impact with the water which sank to the bottom of the ocean on each launch.

Additionally, solid rocket boosters are some of the hardest things to re-use as the process of re-filling them is more like re-manufacturing them than actual true re-use. The sections (they had 4 sections) need to disassembled and refilled with the epoxy that is the solid rocket fuel. They were additionally made of steel rather than aluminum so were not substantially valuable components to recover versus the high end aluminum alloys in the external tanks.

Landing the rocket back on the pad requires significantly more fuel for most missions. The reason most Falcon 9s do landing at sea instead of RTLS is due to this. They have to boost up and out over the ocean to the correct insertion coordinates, and then they run out of fuel (for the mission). When they run out of mission fuel, they just use gravity and fall straight downwards to land on a drone ship.

In short, performing RTLS requires additional fuel. This is fuel that can no longer be used to boost the payload into the correct orbital insertion. So all RTLS missions tend to be lower performance missions that don't need the full power of the Falcon 9 / Heavy since they have fuel to spare for RTLS.

Right, for the Space Shuttle the shortest interval on a back-to-back mission was 63 days.

And I believe that the Falcon 9 with the fastest turnaround was B1062 with 21 days between flights. The previous record (also from a Falcon 9) was two separate boosters who launched and relaunched 27 days apart.

> The innovation here isn't about reusability at all, it's about the economics of reuse.

It's about both.

SpaceX showed that the 1st stage of a rocket can be reliably reused in production. Which is really important from an architecture perspective because 2/3 stage rockets are just more efficient than 1/1.5 stage rockets (mostly due to the propellant mass fraction term of the rocket equation).

To give some examples, the payload mass fraction of some reusable rockets is:

* Shuttle(partial reuse): 1%

* Falcon 9(partial reuse): 4%

* Starship(full reuse, in development): 2%

To be fair to the older models, I think the main issue is: only "recently" (let's say, some 30yrs ago), we have had computers and sensors fast enough to manage an automated reentry of rocket stages (and ship drones as well)

And SpaceX had to iterate a lot to get this working as well

It is rocket science

The older model also didn't incentivize the things needed to support a reusable rocketry program. Companies were encouraged to have bloat and making satellites was still extremely expensive so there wasn't anywhere near enough demand to justify producing and reusing a handful of boosters.

Ariane space was still arguing that reuse wasn't viable for them due to their low flight rate only until a handful of years ago. As far as I'm aware, ULA's CEO still insists that anything more than their proposed engine segment reuse is going to require too high of a flight rate to pay for itself (IIRC he said they'd need 10 flights per booster).

This is also part of why SpaceX's model works. Even when disposable F9 is much cheaper than previous rockets in its class.

>The older model also didn't incentivize the things needed to support a reusable rocketry program.

I assume you mean the cost-plus contracting model? Or is there a different incentive mechanism you're referring to?

Cost-plus is part of it, but also just the launch vehicle acquisition process in general.

Early on, SpaceX's biggest hurdle was getting payload contracts. IIRC they had to sue the government several times to overturn bad acquisition policies. Government acquisition processes weren't suited to supporting small new entrances into the launch market and there was somewhat of a belief that you weren't a credible launch provider unless you were as large as Boeing or Lockmart.

In comparison nowadays it's relatively normal for lower cost programs or ones which can accept some loss to try flying on less proven rockets. New bold approaches to designing, building and flying rockets aren't immediately dismissed as just young naive engineers who haven't had the reality of spaceflight beat into them.

What was determined to be bad acquisition policy?

My understanding is that early contracts were awarded to ULA because SpaceX wasn't certified for military payloads. That, combined with your statement, implies the certification process levies bad requirements. Do we know what these bad requirements were?

As Musk had pointed out at the time, the requirements were essentially just large amounts of paperwork (since if NASA considers F9 reliable enough for cargo and even crew, it's kind of ridiculous to suggest it can't handle a GPS satellite), such that it was unreasonable for USAF to buy multiple years worth of launches without competitive bidding despite obviously having another option almost through certification. At the time they had made that award, SpaceX was already mostly through the certification paperwork with zero changes needed to the rocket.

Besides that, although not a lawsuit, Lori Garver's book "Escaping Gravity" goes into a lot of depth regarding the behind the scenes political struggle regarding commercial cargo and commercial crew and how Congress and some parts of NASA leaned on the idea that they couldn't tolerate any failure as a means of trying to disqualify anyone but ULA,Boeing etc from those programs.

I was wrong about them having to sue "several times" though.

A small nit: the DoD and NASA are two different customers who don't have to align on their risk thresholds. Just because NASA is okay with a particular risk, doesn't mean that the DoD should be. What I've seen happen in some cases is one side essentially says "That may be okay for them, but we don't trust their level of oversight and want it done our way." I would push back a bit on the "mostly certified" as being sufficient; you're either certified or you're not.

I've seen the paperwork argument cut both ways. It can definitely create a bureaucratic mess. On the other hand, one of the things NASA tries to drive is "risk informed decision making". Part of this process involves writing waivers when a requirement can't/won't be met to document what the new risk is (and they have to document that they find that risk acceptable). A lot of times, this process was dismissed at "just large amounts of paperwork" but in dismissing it, they made it very hard for decision makers to fully understand what the residual risk was. It was interesting to me that paperwork was used as an excuse to not commit to the process, but when it was streamlined, it still wasn't used. To me, that feels more like avoiding accountability than avoiding needless paperwork. This misunderstanding of risk is at the heart of most of NASA's spaceflight mishaps.

I wasn't aware of Garver's book, but thanks for bringing it up. Sounds like a good read.

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