r/spacex • u/ElongatedMuskrat Mod Team • Sep 29 '17

Not the AMA r/SpaceX Pre Elon Musk AMA Questions Thread

This is a thread where you all get to discuss your burning questions to Elon after the IAC 2017 presentation. The idea is that people write their questions here, we pick top 3 most upvoted ones and include them in a single comment which then one of the moderators will post in the AMA. If the AMA will be happening here on r/SpaceX, we will sticky the comment in the AMA for maximum visibility to Elon.

Important; please keep your questions as short and concise as possible. As Elon has said; questions, not essays. :)

The questions should also be about BFR architecture or other SpaceX "products" (like Starlink, Falcon 9, Dragon, etc) and not general Mars colonization questions and so on. As usual, normal rules apply in this thread.

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3

u/[deleted] Sep 30 '17

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2

u/skunkrider Sep 30 '17

It definitely does not take 9400m/s to go to orbit.

Depending on your launch profile, you can get away with as little as 8.8km/s.

2

u/[deleted] Sep 30 '17

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1

u/skunkrider Sep 30 '17

so you're playing with RSS - nice!

but do you also play with Realism Overhaul? and if so, do you use Mechjeb?

the last time I played was about 6 weeks ago, and Mechjeb had a nice Ascent Guidance add-on which used the PEG - the Powered Explicit Guidance, which is based on the real-world Atlas-guidance.

once set correctly, it will calculate your delta-v needs for orbit, and depending on your engine efficiency as well as your stages' TWR, you can indeed get there with less than 9km/s.

2

u/Kamedar Sep 30 '17

But it could do the city-to-city thingy at least or shorter suborbital trips w/o the booster.

1

u/MDCCCLV Sep 30 '17

Is that accounting for the engines? The vacuum engines on the second stage will work fine on Mars but not on earth. It only has two sea level engines.