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Comment by zaroth | Hacker News Reader

Not sure if overshot is the right word, I read the final burn was programmed to just empty the tanks, and they would get however far they could.

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This is true. The engines overperformed and they're going a lot further than they meant to. This is better than anticipated news.

It's only bad if you're REALLY focused on the Tesla "going to Mars", which it was never really going to do, because it would need to slow down once it got to Mars to stay in orbit around it. What we've done is prove capability. Getting to Mars is 100% possible, and we've also proven fault tolerance ... that is, we have enough fuel to spare that we can make correction-burns if necessary during the trip to Mars.

I wonder if the right transfer orbit, combined with a gravity assist, could put something into Mars orbit without further thrust.

Really itching to install some Kerbal Space Program mods and try to figure it out...

I was thinking of right transfer orbit combined with exactly right aerobraking, though I'm not sure if Mars has a dense enough atmosphere even if you were aiming for a flyby 1 millimeter above the surface (and that's assuming an indestructible Roadster)...

From Musk's talk on the BFR he says the atmosphere of mars will be sufficient to remove 99% of the ship's momentum before the rockets kick in.

https://www.youtube.com/watch?v=GWQ0jBKH36Y

There's one YouTuber who does car ramp jumps between different bodies in the Kerbal system!

I think it would have been pretty feasible, but the earliest opportunity is in May.

You need a third body to pull that off, and I think Mars’s moons are too small to be useful for this.

Looking at practical considerations rather than just theoretical, you also need the ability to perform course corrections along the way. The initial trajectory won’t be precise enough to make it work from just the departure burn.

There's a gravity assist mod for KSP?!

KSP has gravity assist built in: it's an expected consequence of newtonian physics (Which KSP models).

Mods might be to swap to the Solar rather than Kerbol system, etc.

Yep. Real-Scale Solar System provides that. There are also mods to add real-world rockets (like the Falcon Heavy) and real-world aerodynamics (Ferram Aerospace Research).

Well, it's time I fire up KSP again!

To do a gravity assist you do not need anything more than Newtonian two-body interaction. KSP already has that.

You can think of it as a small ball (the vehicle) bouncing of a big heavy ball (the planet), but the forces are not those of elastic compression, rather those of gravity.

> Really itching to install some Kerbal Space Program mods and try to figure it out...

If someone doesn't add a Tesla Roadster mod to the VAB I'll be extremely disappointed in the entire modding community.

Or carry more mass, the car didn't even have a roof

None of the Roadsters did, as far as I know.

Tesla roadster has targa roof. You install it manually when you want.

> it would need to slow down once it got to Mars to stay in orbit around it.

I don't think orbiting mars was ever the plan. They were talking about a mars orbit, meaning an orbit of the sun at about the distance of mars.

You're agreeing with his point. The plan was not to orbit Mars.

However, your language sounds like they were going to circularize at 'about the distance of mars', which they were not (that too would have required a burn months from now). The plan they'd previously briefed was an elliptical orbit where the aphelion is ~Mars' orbitial distance (~1.5AU) and the perihelion is still at Earth's orbital distance (~1AU). However, with the extended burn, they got the aphelion up to 2.61 AU.

> that is, we have enough fuel to spare that we can make correction-burns if necessary during the trip to Mars.

Stage 2 of the Falcon would not be used for long flights. This was the longest it ever coasted (6 hours). Any longer, and you run into all sorts of limitations: running out of batteries, RP-1 freezing, and LOX boiling off.

For longer trips, stage 2 would separate after the earth escape burn and the craft's own propulsion system would take over.

It's overshot in the sense that the PR materials they released showed it making a perfect Mars transfer orbit. Apparently Musk said "If the third burn goes as we hope, the Tesla will get as far away as 380 to 450 million km from Earth." Their aphelion is right around 390 500 000km, so just a bit above the lower bound.

Distance from Earth and solar aphelion aren't the same thing. The former will be larger by 300 million km (the diameter of Earth's orbit) when Earth is on the opposite side of the sun. It's unclear which value Musk was referring to.

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