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Comment by samishxc | Hacker News Reader

In what ways will this be useful? I imagine if a rocket carries a payload into space it wouldn't be able to land vertically like this, or is that the intention?

Either way, very interesting

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It is important to keep in mind that the fuel costs for bringing a stage back down are far lower than the cost to put it up there, since most of the mass (fuel) will be burnt off before the return leg starts.

Since fuel is the cheap part anyway, Space X is betting that they can make it economically sound to launch a bit more fuel than they would normally need to if it means they can get the (expensive) rocket stage back.

Fly to Mars (or anywhere else in the solar system), land, unload passengers and cargo, refuel, take off again, fly to Earth, land. Refuel and start loading for the next flight.

That's the end goal. And since not all bodies SpaceX may want to land on have a comparable atmosphere to Earth, parachutes are not part of the plan.

This isn't the vehicle that's going to do all that, but they have to start somewhere to build the tech that eventually will.

More like: launch to earth orbit (dropping the first and second stages, that land at spaceports for shipping home and refuelling), dock to a larger ship (nuclear?) which carries them to Mars, un-dock in Mars orbit and make a powered descent to the colony there. And then do the whole thing again backwards.

I doubt this vehicle will be used for landing on Earth(why not use parachutes?). I would rather send it to Mars orbit and reuse it there as a landing module, but not take it back to Earth.

Why not use chutes? Because with rockets, you can steer, and fine-tune the rate of descent. You don't need to splash down at sea, you can land on solid ground, and pick which bit of ground to land on (such as a spaceport). It's less of a bumpy ride and cheaper to recover.

The auxiliary solid fuel rockets of the space shuttle slashed in the sea with parachutes and were "reusable". But they were so bumped that the refurbishment procedure involved a lot of handwork and iirc more than a month.

The intention is to make both stages of the Falcon 9 reusable and to have them land vertically back at the launch site. This does add weight, for thermal protection and landing gear, and it uses up some propellant but on the whole the savings in capital and operational costs should more than make up for it. Right now the entire rocket is thrown away for every launch, which is hugely expensive. But if they can manage to get dozens of launches out of each vehicle then they can reduce costs by a huge margin even if payload is cut in half or worse.

The objective is to have reusable stages. Instead of letting them burn up in the atmosphere, they land vertically to be reused.

Typically the first stage is destroyed during impact with the water(or ground). The Shuttle SRBs were generally recovered undamaged, but relied on large parachutes and were towed back using a specialized ship.

SpaceX Grasshopper avoids either destroying the first stage, or a labor intensive and expensive recovery process.

The SRBs were generally recovered bent or squished. There was actually a machine to bend the stack segments back to round.

Do you have a reference for that? I thought the SRB segments are quite structurally strong and the parachutes quite large and effective.

> Do you have a reference for that?

No, but I'm sure I read that right and the machine existed.

> I thought the SRB segments are quite structurally strong and the parachutes quite large and effective.

They are, but the stresses are large, the diameter is large, and the requirements quite stringent. If a casing is out of round by a small fraction, this might still cause the o-rings to not be pressed against the casings tightly enough.

Like the other commenters gave said, landing vertically is very much their intention. The rationale is that sea landings make repair work much harder.

> The rationale is that sea landings make repair work much harder.

Ist the much more importend things the time and cost of getting the rocket back to where you want it much bigger?

I imagine that's a factor, but it's primarily the fact that sea water is really hard on the delicate parts of the rocket due to corrosion and mineral deposits.

And very rapid cooling as well as the chance of impact damage. Sea landings may look gentle but really they aren't.

then wouldn't it make more sense to just build a very big pool/use an unsalty lake ?

You'd still need to steer the rocket there but you can avoid worrying about vertical landing.

There was an SSTO proposal from the 1970's that did involve building a huge splashdown lake. That proposal also used vertical landing, however. (The craft was so large, landing gear would've been prohibitive, so the whole thing just floated.)

Mars does not currently have lakes.

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Fourth, don’t be mean. I think you are part of the problem, honestly. (As am I, admittedly.)

Merry Christmas!

Had a few too many!? As the Hacker News Pro you claim to be you definitely did not find the right tone or even the right comment to reply to...

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