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I hope one day soon we can use a SpaceX Starship super heavy to accelerate a probe at much higher velocities. The only thing is, unlike rockets, there is little

by hliyan 6y ago

I hope one day soon we can use a SpaceX Starship super heavy to accelerate a probe at much higher velocities. The only thing is, unlike rockets, there is little incentive for private companies to invest in producing better, cheaper space probes.

7373737373 6y ago
I'd love to see an estimation of how expensive such a project would be/how long it would take to overtake the Voyagers distance wise.
- Denvercoder9 6y ago
  It's unlikely to happen. Using the numbers from Wikipedia for Starship, for a 5 ton payload the first stage has a delta-v of 3.8km/s and the second stage of 8.8km/s. That gives only 12.6km/s in total, while Voyager had around 20km/s after its departure from Earth. Even if the Starship is fully refueled in orbit to give it another boost (and we don't want to recover it), we get only 21.4km/s. However, the Voyagers got a gravity assist from all the outer planets, where they gained even more speed. That's only possible if they are all aligned, which happens only once every 175 years. That's also the reason why New Horizons, the Pluto probe launched 30 years later, will never overtake the Voyagers: it's travelling slower because it didn't get to do the gravity assists (even though it was launched at a higher speed from Earth). Also it's important to note that Starship isn't really optimized for such missions due to its high dry mass. It's made to bring a lot of mass to orbit cheaply, not really to accelerate it very fast.
  - gpm 6y ago
    I don't think you use starship as the stage that pushes the probe to escape velocity, you use a ion engine (which spacex also develops for starlink). They're an order of magnitude more efficient... Starship just lifts it to orbit.
    - Denvercoder9 6y ago
      The problem with ion engines is that they need quite a lot of power, which becomes problematic in deep space. Solar panels aren't really viable outside the orbit of Mars. Anyway, yes, of course there are countless variations that can be done to make it work. Sticking a Centaur or two in a Starship also seems to be viable. But the parent comment specifically asked about Super Heavy/Starship here.
      - addaon 6y ago
        Ion engines need a lot of power, but scale down quite well to lower powers and lower thrust. And even with an ion engine, you'd only be running it for a few years at the beginning of a mission. Meanwhile, one of your major power draws is a radio, which needs higher power as distance to Earth increases, later in the mission. Finally, nuclear thermal power supplies have decreasing power budgets over time. It seems reasonable to me that there's a combined power budget with focuses on ion propulsion for the first several years of a probe's lifetime, disabling the ion drive and shifting the (reducing) power budget to comms once target velocity is achieved.
        HeadsUpHigh 6y ago
        Given that the rate of decay of the radioactive material in the RTG is constant the maximum mission time is set in stone from the beginning and can't be extended( i.e. it's a property of the material).
TeMPOraL 6y ago
The private sector can't be expected to do everything, but the availability of Starship will change such high-velocity probes from "not affordable" to merely "somewhat expensive".
jniedrauer 6y ago
Most of the escape velocity of the voyager probes came from a gravitational slingshot around the gas giants. I don't think additional rocket power would help much.
mdorazio 6y ago
Some quick napkin math based on rough numbers: Starship estimated payload to LEO: 100 t Voyager mass: 1,820 lb Booster: let's assume an ideal state of 1 Raptor engine (3,300 lb) and 5,000 lb of other stuff before fuel Plugging into the rocket equation and assuming no further staging, that gets us a delta v of 89,428 mi/hr, or about 2.3x the speed of Voyager 1. I'm not sure if we should add the orbital speed of Earth to that or not. Also keep in mind that the Voyagers reached their speeds thanks to several gravity slingshots, so in theory we could boost our Starship speedball probe even higher than that. If we used a fat Ion engine instead of chemical rockets, we'd get a lot more delta v as well (although over the course of years instead of a few minutes).
- HeadsUpHigh 6y ago
  Ion engines is the only way a mission like this makes sense. Chemical rockets just don't cut it as much. Also what isp did you use? The vacuum raptor has significantly higher isp compared to the sea level one( and I'm not even sure that you can operate a sea raptor in vacuum).

by hliyan 6y ago

7373737373 6y ago

I'd love to see an estimation of how expensive such a project would be/how long it would take to overtake the Voyagers distance wise.

Denvercoder9 6y ago
It's unlikely to happen. Using the numbers from Wikipedia for Starship, for a 5 ton payload the first stage has a delta-v of 3.8km/s and the second stage of 8.8km/s. That gives only 12.6km/s in total, while Voyager had around 20km/s after its departure from Earth. Even if the Starship is fully refueled in orbit to give it another boost (and we don't want to recover it), we get only 21.4km/s. However, the Voyagers got a gravity assist from all the outer planets, where they gained even more speed. That's only possible if they are all aligned, which happens only once every 175 years. That's also the reason why New Horizons, the Pluto probe launched 30 years later, will never overtake the Voyagers: it's travelling slower because it didn't get to do the gravity assists (even though it was launched at a higher speed from Earth). Also it's important to note that Starship isn't really optimized for such missions due to its high dry mass. It's made to bring a lot of mass to orbit cheaply, not really to accelerate it very fast.
- gpm 6y ago
  I don't think you use starship as the stage that pushes the probe to escape velocity, you use a ion engine (which spacex also develops for starlink). They're an order of magnitude more efficient... Starship just lifts it to orbit.
  - Denvercoder9 6y ago
    The problem with ion engines is that they need quite a lot of power, which becomes problematic in deep space. Solar panels aren't really viable outside the orbit of Mars. Anyway, yes, of course there are countless variations that can be done to make it work. Sticking a Centaur or two in a Starship also seems to be viable. But the parent comment specifically asked about Super Heavy/Starship here.
    - addaon 6y ago
      Ion engines need a lot of power, but scale down quite well to lower powers and lower thrust. And even with an ion engine, you'd only be running it for a few years at the beginning of a mission. Meanwhile, one of your major power draws is a radio, which needs higher power as distance to Earth increases, later in the mission. Finally, nuclear thermal power supplies have decreasing power budgets over time. It seems reasonable to me that there's a combined power budget with focuses on ion propulsion for the first several years of a probe's lifetime, disabling the ion drive and shifting the (reducing) power budget to comms once target velocity is achieved.
      - HeadsUpHigh 6y ago
        Given that the rate of decay of the radioactive material in the RTG is constant the maximum mission time is set in stone from the beginning and can't be extended( i.e. it's a property of the material).

TeMPOraL 6y ago

The private sector can't be expected to do everything, but the availability of Starship will change such high-velocity probes from "not affordable" to merely "somewhat expensive".

jniedrauer 6y ago

Most of the escape velocity of the voyager probes came from a gravitational slingshot around the gas giants. I don't think additional rocket power would help much.

mdorazio 6y ago

Some quick napkin math based on rough numbers: Starship estimated payload to LEO: 100 t Voyager mass: 1,820 lb Booster: let's assume an ideal state of 1 Raptor engine (3,300 lb) and 5,000 lb of other stuff before fuel Plugging into the rocket equation and assuming no further staging, that gets us a delta v of 89,428 mi/hr, or about 2.3x the speed of Voyager 1. I'm not sure if we should add the orbital speed of Earth to that or not. Also keep in mind that the Voyagers reached their speeds thanks to several gravity slingshots, so in theory we could boost our Starship speedball probe even higher than that. If we used a fat Ion engine instead of chemical rockets, we'd get a lot more delta v as well (although over the course of years instead of a few minutes).

HeadsUpHigh 6y ago
Ion engines is the only way a mission like this makes sense. Chemical rockets just don't cut it as much. Also what isp did you use? The vacuum raptor has significantly higher isp compared to the sea level one( and I'm not even sure that you can operate a sea raptor in vacuum).