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SpaceX Interplanetary Transport System: https://www.youtube.com/watch?v=0qo78R_yYFA https://www.youtube.com/watch?v=0qo78R_yYFA

by Rezo 10y ago

sandis 10y ago
"The video appears to show SpaceX's new rocket — the BFR, or "Big Fucking Rocket" — as well as the company's interplanetary spaceship — the BFS, or "Big Fucking Spaceship.""
- Gravityloss 10y ago
  I prefer the Big Friendly Rocket interpretation. :)
  - mparlane 10y ago
    SpaceX refer to it as Big Falcon Rocket
hoorayimhelping 10y ago
28 million pounds of thrust is 4 times what the Saturn V was capable of.
Gravityloss 10y ago
Unconventional design. The rocket looks very large and they mention 120 million newtons takeoff thrust so the weight is about 10 million kg, 3 times Saturn V size. The first stage lands back on launch stool, the tanker stage is put on top of it and it launches again. This implies a relatively fast turnaround. Both the second stage and the tanker seem to have complete heat shields and stub wings and ability to re-enter either Mars or Earth. So all parts 1) big 2) landable and 3) short turnaround time This would imply they will launch them a lot, so they're really ramping up the traffic to Mars, not just a few missions? I don't understand the 100 000 km/h which is 30 km/s speed for the Mars cruise. Would be really hard to achieve with chemical propulsion. With 4 km/s exhaust velocity and delta vee of say 20 km/s you get a required mass ratio of e^(20/4) which is 150. And they lug the upper stage engines all the way, and there's heatshield and wings. Impossible. Also the 200 kW electrical power advertised is puny for electrical propulsion. With an ISP of 1000 (exhaust 10 km/s) you get an 20 Newtons of thrust [correction from 200N], which is nothing for their ship size. If they only have ten tons of mass, then it takes 200 days to accelerate to full speed. Typically you might need 10 to 20 km/s speed for Mars. Their plan does not compute for me. EDIT: So it can work if they only go for 10 km/s.
- pinewurst 10y ago
  Speed to Mars though is really relative speed along whatever orbit (Hohmann transfer or the moral equivalent) that you choose. Only in SF stories do we have fully powered propulsion to Mars. I am very curious what the selected family of orbits is, and even more importantly how long & how much life support for the large passenger number.
  - twoodfin 10y ago
    Yeah, transit time & payload mass seem to be the major missing numbers in a video that wasn't shy about including them.
    - codeulike 10y ago
      Average 115 days, payload to Mars 450 tonnes. 100 people he reckons.
    - jonknee 10y ago
      There's a slide with all the numbers and even a graph: https://youtu.be/A1YxNYiyALg?t=1h52s https://youtu.be/A1YxNYiyALg?t=1h52s
  - exDM69 10y ago
    > I am very curious what the selected family of orbits is ... There's not much leeway, it's going to be something close to a Hohmann transfer, with the aphelion ahead of and above Mars to get to a hyperbolic capture orbit with the periareion deep in the atmosphere for (almost) direct re-entry. This kind of orbits can be solved for arbitrary departure date and time of flight using a Lambert's problem solver and numerical optimization. Not a particularly difficult problem by modern standards. Pure Hohmann transfer to another planet will result in inevitable collision due to relative velocity, but it's useful for lower bound estimates. Another alternative for recurring Mars intercept is is the "Aldrin cycler" (after Buzz Aldrin) which is a free return trajectory but that is difficult when the goal is to land and take off again. There are lots of possibilities for lower energy transfers but most of them are out of question when life support is required for humans on board.
JumpCrisscross 10y ago
Why do they launch the passengers first? Passengers eat and shit and breathe while they wait. They're also liable to be more upset if their mission is aborted, due to a failed tanker launch, while they're in orbit.
- tempestn 10y ago
  If they do, I assume because it's easier to transfer fuel than passengers.
- yincrash 10y ago
  I believe his answer in the QA was that you would launch an empty rocket first, and once that rocket is fueled, a 2nd rocket with passengers would launch and transfer to the fueled rocket, and then the new passenger-empty rocket would be in orbit to be fueled for the next trip.
- Nashhhh 10y ago
  In the Q&A part he addresses this. I think they showed passengers first for the video just for stylistic purposes. He said he thinks you'd probably be launching spaceships and begin fueling between trips (26 months), keeping them parked in orbit, and then passengers would go up last before the trip and board fully fuled ships. I think it's a detail that's not determined yet. Watch the video.
- shkkmo 10y ago
  In the QA he clarifies that they are unsure about refueling time, it might be that they launch a vehicle, refuel it, and then launch another vehicle with passengers, then transfer those passengers to the refueled vehicle. It depends on refueling time.
Symmetry 10y ago
My reaction, after thinking about this for a bit, is more "This is going to be everything the Shuttle was supposed to be!" than anything to do with getting people to Mars. That's all, of course, predicated on getting the turnaround for this thing fast and cheap. With orbital refueling I wonder how much one of these could land on the Moon?

SpaceX Interplanetary Transport System: https://www.youtube.com/watch?v=0qo78R_yYFA https://www.youtube.com/watch?v=0qo78R_yYFA

by Rezo 10y ago

SpaceX Interplanetary Transport System: https://www.youtube.com/watch?v=0qo78R_yYFA https://www.youtube.com/watch?v=0qo78R_yYFA

sandis 10y ago

"The video appears to show SpaceX's new rocket — the BFR, or "Big Fucking Rocket" — as well as the company's interplanetary spaceship — the BFS, or "Big Fucking Spaceship.""

Gravityloss 10y ago
I prefer the Big Friendly Rocket interpretation. :)
- mparlane 10y ago
  SpaceX refer to it as Big Falcon Rocket

hoorayimhelping 10y ago

28 million pounds of thrust is 4 times what the Saturn V was capable of.

Gravityloss 10y ago

Unconventional design. The rocket looks very large and they mention 120 million newtons takeoff thrust so the weight is about 10 million kg, 3 times Saturn V size. The first stage lands back on launch stool, the tanker stage is put on top of it and it launches again. This implies a relatively fast turnaround. Both the second stage and the tanker seem to have complete heat shields and stub wings and ability to re-enter either Mars or Earth. So all parts 1) big 2) landable and 3) short turnaround time This would imply they will launch them a lot, so they're really ramping up the traffic to Mars, not just a few missions? I don't understand the 100 000 km/h which is 30 km/s speed for the Mars cruise. Would be really hard to achieve with chemical propulsion. With 4 km/s exhaust velocity and delta vee of say 20 km/s you get a required mass ratio of e^(20/4) which is 150. And they lug the upper stage engines all the way, and there's heatshield and wings. Impossible. Also the 200 kW electrical power advertised is puny for electrical propulsion. With an ISP of 1000 (exhaust 10 km/s) you get an 20 Newtons of thrust [correction from 200N], which is nothing for their ship size. If they only have ten tons of mass, then it takes 200 days to accelerate to full speed. Typically you might need 10 to 20 km/s speed for Mars. Their plan does not compute for me. EDIT: So it can work if they only go for 10 km/s.

pinewurst 10y ago
Speed to Mars though is really relative speed along whatever orbit (Hohmann transfer or the moral equivalent) that you choose. Only in SF stories do we have fully powered propulsion to Mars. I am very curious what the selected family of orbits is, and even more importantly how long & how much life support for the large passenger number.
- twoodfin 10y ago
  Yeah, transit time & payload mass seem to be the major missing numbers in a video that wasn't shy about including them.
  - codeulike 10y ago
    Average 115 days, payload to Mars 450 tonnes. 100 people he reckons.
  - jonknee 10y ago
    There's a slide with all the numbers and even a graph: https://youtu.be/A1YxNYiyALg?t=1h52s https://youtu.be/A1YxNYiyALg?t=1h52s
- exDM69 10y ago
  > I am very curious what the selected family of orbits is ... There's not much leeway, it's going to be something close to a Hohmann transfer, with the aphelion ahead of and above Mars to get to a hyperbolic capture orbit with the periareion deep in the atmosphere for (almost) direct re-entry. This kind of orbits can be solved for arbitrary departure date and time of flight using a Lambert's problem solver and numerical optimization. Not a particularly difficult problem by modern standards. Pure Hohmann transfer to another planet will result in inevitable collision due to relative velocity, but it's useful for lower bound estimates. Another alternative for recurring Mars intercept is is the "Aldrin cycler" (after Buzz Aldrin) which is a free return trajectory but that is difficult when the goal is to land and take off again. There are lots of possibilities for lower energy transfers but most of them are out of question when life support is required for humans on board.

JumpCrisscross 10y ago

Why do they launch the passengers first? Passengers eat and shit and breathe while they wait. They're also liable to be more upset if their mission is aborted, due to a failed tanker launch, while they're in orbit.

tempestn 10y ago
If they do, I assume because it's easier to transfer fuel than passengers.
yincrash 10y ago
I believe his answer in the QA was that you would launch an empty rocket first, and once that rocket is fueled, a 2nd rocket with passengers would launch and transfer to the fueled rocket, and then the new passenger-empty rocket would be in orbit to be fueled for the next trip.
Nashhhh 10y ago
In the Q&A part he addresses this. I think they showed passengers first for the video just for stylistic purposes. He said he thinks you'd probably be launching spaceships and begin fueling between trips (26 months), keeping them parked in orbit, and then passengers would go up last before the trip and board fully fuled ships. I think it's a detail that's not determined yet. Watch the video.
shkkmo 10y ago
In the QA he clarifies that they are unsure about refueling time, it might be that they launch a vehicle, refuel it, and then launch another vehicle with passengers, then transfer those passengers to the refueled vehicle. It depends on refueling time.

Symmetry 10y ago

My reaction, after thinking about this for a bit, is more "This is going to be everything the Shuttle was supposed to be!" than anything to do with getting people to Mars. That's all, of course, predicated on getting the turnaround for this thing fast and cheap. With orbital refueling I wonder how much one of these could land on the Moon?