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Interstellar Probe, a Mission Concept for NASA

73 points by CrankyBear 7y ago

xt00 7y ago
Summary: burn lots of fuel to go to periphery of solar system, dive back toward the sun and skim it very closely to maximize velocity and use a bunch of fuel next to the sun at max V (oberth maneuver) https://en.m.wikipedia.org/wiki/Oberth_effect https://en.m.wikipedia.org/wiki/Oberth_effect and then go hurtling out of solar system.. main challenge is solar shielding.. the deeper into the gravity well you can go the faster you can go due to the deltaV performed next to the sun..
- deleted 7y ago
  [deleted]
- pdonis 7y ago
  It looks like the initial outward leg would only be to Jupiter; the idea appears to be to use a gravity assist around Jupiter to get more velocity diving towards the Sun. It doesn't make sense to me to use very much fuel trying to get farther out from the Earth before diving in towards the Sun; the additional speed just from the increased distance of fall is negligible, and you could take the same fuel and burn it during the Oberth maneuver at the Sun to get more bang for the buck out of it. It might be worth it for the additional speed from a Jupiter gravity assist if things were aligned just right.
  - thatcherc 7y ago
    The reason for a detour to Jupiter is that it's actually fairly hard to get closer to the Sun. Somewhat surprisingly (if you haven't seen it before), it takes quite a bit of energy to drop from Earth's orbit around the Sun to ie Mercury's. In this case, it looks like it would take less energy to fly out to Jupiter and get the gravity assist (which is very substantial because of the planet's mass), and fall back toward the Sun than it would be to drop straight into a low solar orbit from Earth. This type of trajectory was actually considered for the Parker Solar Probe [0], but was eventually rejected because it would take too long.* If you're going on an interstellar voyage, the time to get out to Jupiter might not impact the timeline as much. [0] - https://wikipedia.org/wiki/Parker_Solar_Probe https://wikipedia.org/wiki/Parker_Solar_Probe * notably, the new trajectory still includes gravity assists off Earth and Venus, underscoring the amount of delta-V needed to lower a solar orbit
    - xt00 7y ago
      Yea interesting! Parker solar probe will hit a whopping 0.064% of the speed of light.. and the orbit is quite interesting as you said — needs to slow down to cancel out the speed of earths orbital velocity. So ya know, for a reference point, the 1% of the speed of light that the Trisolaran fleet is flying at is just a mere 6.7 billion miles per hour.. so 0.5 million ain’t too bad...
      - thatcherc 7y ago
        Always good to have the Trisolarans to put things in perspective! Just gotta watch out for those pesky droplets...
        topkeks 7y ago
        And that fucking sophon block...
    - pdonis 7y ago
      > it takes quite a bit of energy to drop from Earth's orbit around the Sun to ie Mercury's More precisely, you have to lose a significant amount of energy relative to the Sun, and it takes significant delta-v for a spaceship starting at Earth (to cancel out at least part of Earth's orbital speed about the Sun) to do that. Yes, that's a valid point.
- the_pwner224 7y ago
  With some more detail on the mechanics: Here's a screenshot of an orbit in Kerbal Space Program, an excellent NASA-simulator game (you have a spaceport and make + fly rockets and do science): https://wiki.kerbalspaceprogram.com/wiki/File:KerbalEccentricity.jpg https://wiki.kerbalspaceprogram.com/wiki/File:KerbalEccentri... On the blue orbit, you can see Ap and Pe. Ap is the apogee; the place in the orbit where the spacecraft is closest to the earth. Pe is the perigee, the place where the spacecraft is farthest from the earth. Since the blue orbit is mostly circular, they are at about the same altitude. If you look at the large white orbit, the apogee would be the leftmost point, close to the apogee of the blue orbit. The perigee would be all the way at the right of the image. When your spacecraft is at position X, thrusting your engines will not meaningfully change your current position - the acceleration they generate is negligible to the speed at which you are moving. However, the maneuver will change your speed, which affects your orbit. At the apogee, if you thrust in the direction you are moving, your perigee will increase - the orbit will become even more eccentric. Example: at the apogee you are moving at 100 miles per second. Thrusting the engines will not change your current position much; your current position is determined by your 100 miles per second speed and where you came from. But the maneuver will change your speed to 105 miles per second, which will cause your perigee to become much farther away from the earth. However your apogee will stay in the exact same position. Why? Because in orbit you are basically flying sideways while gravity pulls you down. In a circular orbit this balances out into you flying around in a circle. But if you go faster, you're going more sideways while gravity pulls the same amount. So your orbit becomes more elongated. You can thrust in the direction of movement at any point in orbit, and it will increase the altitude of the orbit on the opposite side of where you are at - if you thrust at apogee the perigee altitude increases, and in the white elongated orbit if you thrust between the apogee and perigee your orbit will become more circular and bigger. Similarly to make an eccentric orbit circular, you get to the apogee and then use the engines to slow down, which brings down the perigee. Since thrusting changes your position on the opposite side of the orbit, the most efficient way to increase your perigee is to thrust while at the apogee. The NASA thing is basically going into an elongated orbit between the Sun and Jupiter, coming back to the apogee near the Sun, and then thrusting. The difference in efficiency between thrusting at the apogee of an orbit and just thrusting in a straight line out into space is really huge. Though I'm not sure why the extra gravity of the Sun makes the maneuver more efficient. If you're interested in this you should definitely play KSP. It's a great game and gives you a great intuitive sense of how these things work.
- p1mrx 7y ago
  The Oberth effect is interesting. You want to get as low/fast as possible (converting your fuel's gravitational potential energy into kinetic energy), and then do a burn to harvest that energy, dropping the exhaust into the sun while the spacecraft zips away at high speed. It's basically the "tennis ball on a basketball" trick, with rockets.
- mabbo 7y ago
  No matter how it's explained to me, the Oberth effect still seems like magic, or at least some kind of physics violation. Somehow, we use the same delta-V to get more delta-V.
  - greglindahl 7y ago
    You're adding less energy to the exhaust and more to the rocket. The Wikipedia article is a pretty good explanation.
- rbanffy 7y ago
  > main challenge is solar shielding.. If you carry a solar sail to add a little more push from the Sun's radiation you can spare a little material to build a shade on the other side of the sail.
neom 7y ago
I'm no astrophysicist, but I presume the photo would be of the past? Anyone good at math able to say how far in the past a photo would be?
- Sharlin 7y ago
  Well, assuming the probe is even going to carry an imager of any sort. Not much to photograph at 1000 AU. Anyway, 1000 AU equals about 138 light-hours, or 5.7 light-days, so that's how long sunlight would have taken to reach the probe at that distance.
- deleted 7y ago
  [deleted]
- tobylane 7y ago
  5.7 days https://www.wolframalpha.com/input/?i=1000+au+in+light+days https://www.wolframalpha.com/input/?i=1000+au+in+light+days
- mikeash 7y ago
  All photos are of the past.
SiempreViernes 7y ago
Well, that ain't gettin built save for a random political blessing by a young dynasty. Something going the very fastest you can go makes a poor platform for close study of planets, and going very far away negates the great advantage of heliophysics: the sun is right there. You could get all their motivational science, except maybe the exoplanet calibration, done with a slower more modest project. Frankly, if your space experiment has resorted to invoking "inspiring humanity to fight the climate crisis", you can just as well drop the science pretense and fish for money from the astrology community.
themgt 7y ago
The proposal sounds technically interesting, but there seems to be growing skepticism of SLS even within NASA. Everyone from Blue Origin, Arianespace/ESA, China etc are working on reusable rockets while SLS is over budget, behind schedule and looks like it may be effectively obsolete before it's even launching payloads (much less by the time (2025?) NASA can actually procure new "RS-25E" engines rather than using its handful of shuttle leftovers) The most exciting near-future space tech to me is SpaceX's goal to achieve in-orbit refueling with Starship. With their much cheaper reusable launches, you could plausibly put a Starship with payload in low orbit, launch 3-4 tankers to fully refuel it and then blast off to anywhere in or out of the solar system faster than anything now remotely conceivable. You could do a mission like this without the complex gravity assists. SLS is a massive pork program and going to be hard to shut down, but as soon as "BFR"/New Glenn are operational I think it's time to start looking at getting NASA out of the rocket business and focused on cool space/science missions.
- CptFribble 7y ago
  SpaceX has proven that the economics are finally there for private launching. The government should put all the SLS money into the science and extreme boundary-pushing tech research NASA's doing that the economics aren't there for: protections/psych research for long-term space habitation, space farms, probes to the next set of targets (Europa, Titan, interesting asteroids), solar-system scale communications, and orbital manufacturing. NASA laid the groundwork for a larger group of organizations to build on in the earth-to-orbit space. Now NASA should be laying the groundwork for a larger group of organizations to build on in the orbit-to-solar-system space.
- rbanffy 7y ago
  > launch 3-4 tankers to fully refuel it You could also use the tankers to add propellant (not necessarily fuel) to an NTR or an electric thruster with higher Isp than their methalox engines. A couple decades of low thrust would be pretty good.
ta1234567890 7y ago
It's great to see so much interest in space exploration. However, we should put more effort into exploring our own planet. We've literally only scratched the surface. I bet that if we spent even half as much money as we spend on space programs, trying to get to Earth's core, we would advance science and technology a lot faster. Also, we would have a way better idea of how the magnetic field works and how to harness it - maybe we'd even figure out how to have global wireless communication and gps just with underground technology (no satellites needed). It's as if we are traveling across the universe on this amazing organic spaceship (Earth), but we are on the outside. We should figure out what's inside and how to get there.
- whatshisface 7y ago
  Space is pragmatic and cost-effective compared to traveling to the Earth's core.
  - ta1234567890 7y ago
    Maybe now, but it wasn't when people first decided to do it. Also, it might not be now. If we are able to reliably extract energy from lava/volcanoes, we would have enough energy to power the whole world cleanly, which could help immensely with our current climate crisis. Space is a huge expense of energy, which also contributes to the climate crisis. Free/super-cheap global energy sounds like a huge return on investment.
    - mikeash 7y ago
      Space is a negligible amount of energy. Absolutely tiny. I’d wager that GPS alone has made space a net energy positive by saving energy with better routing.
- greglindahl 7y ago
  People can do more than one thing at once. We spend a lot of money studying the Earth, from space and the surface. Studying other planets helps understand things about the Earth that would be difficult to figure out by only studying the Earth. Studying other stars helps us understand the Sun. In another comment you say: > If we are able to reliably extract energy from lava/volcanoes, That's already being done at scale, especially in Iceland.
credit_guy 7y ago
"Interstellar Probe, a mission concept for NASA, aims to travel 93 billion miles past the sun" Comparison to other astronomical distances: * 93 BN miles = 1000 AU (AU = astronomical unit = distance from Sun to Earth) * mean distances from Sun to Neptune and Pluto are roughly 30 AU and 40 AU * current distance from Sun for Voyager 1 and 2: 146 AU and 121 AU (see [1] which is quite cool, these distances are updated real time) * 1000 AU = 1.6% of a light year * 1000 AU = 0.36% of the distance to the closest star Alpha Centauri [1]https://voyager.jpl.nasa.gov/mission/status/ https://voyager.jpl.nasa.gov/mission/status/
aruggirello 7y ago
So if this probe is bound to venture into the distance range useful for a solar gravitational lensing telescope, why not use it to deploy one? That would really be a major breakthrough IMHO. https://arxiv.org/abs/1604.06351 https://arxiv.org/abs/1604.06351 "The minimum distance for a solar lensing telescope is 547 astronomical units (AU). And in reality, proper positioning would likely require the telescope to be placed even farther out — perhaps as far as 2,000 AU or more."
rbanffy 7y ago
I always wonder what would be the fastest spacecraft we could build for a given mass budget. NASA should host a competition for designs that could reach one light day/month/year in the shortest time under a given mass constraint using existing or reasonably extrapolated technology.

73 points by CrankyBear 7y ago

xt00 7y ago

Summary: burn lots of fuel to go to periphery of solar system, dive back toward the sun and skim it very closely to maximize velocity and use a bunch of fuel next to the sun at max V (oberth maneuver) https://en.m.wikipedia.org/wiki/Oberth_effect https://en.m.wikipedia.org/wiki/Oberth_effect and then go hurtling out of solar system.. main challenge is solar shielding.. the deeper into the gravity well you can go the faster you can go due to the deltaV performed next to the sun..

deleted 7y ago
[deleted]
pdonis 7y ago
It looks like the initial outward leg would only be to Jupiter; the idea appears to be to use a gravity assist around Jupiter to get more velocity diving towards the Sun. It doesn't make sense to me to use very much fuel trying to get farther out from the Earth before diving in towards the Sun; the additional speed just from the increased distance of fall is negligible, and you could take the same fuel and burn it during the Oberth maneuver at the Sun to get more bang for the buck out of it. It might be worth it for the additional speed from a Jupiter gravity assist if things were aligned just right.
- thatcherc 7y ago
  The reason for a detour to Jupiter is that it's actually fairly hard to get closer to the Sun. Somewhat surprisingly (if you haven't seen it before), it takes quite a bit of energy to drop from Earth's orbit around the Sun to ie Mercury's. In this case, it looks like it would take less energy to fly out to Jupiter and get the gravity assist (which is very substantial because of the planet's mass), and fall back toward the Sun than it would be to drop straight into a low solar orbit from Earth. This type of trajectory was actually considered for the Parker Solar Probe [0], but was eventually rejected because it would take too long.* If you're going on an interstellar voyage, the time to get out to Jupiter might not impact the timeline as much. [0] - https://wikipedia.org/wiki/Parker_Solar_Probe https://wikipedia.org/wiki/Parker_Solar_Probe * notably, the new trajectory still includes gravity assists off Earth and Venus, underscoring the amount of delta-V needed to lower a solar orbit
  - xt00 7y ago
    Yea interesting! Parker solar probe will hit a whopping 0.064% of the speed of light.. and the orbit is quite interesting as you said — needs to slow down to cancel out the speed of earths orbital velocity. So ya know, for a reference point, the 1% of the speed of light that the Trisolaran fleet is flying at is just a mere 6.7 billion miles per hour.. so 0.5 million ain’t too bad...
    - thatcherc 7y ago
      Always good to have the Trisolarans to put things in perspective! Just gotta watch out for those pesky droplets...
      - topkeks 7y ago
        And that fucking sophon block...
  - pdonis 7y ago
    > it takes quite a bit of energy to drop from Earth's orbit around the Sun to ie Mercury's More precisely, you have to lose a significant amount of energy relative to the Sun, and it takes significant delta-v for a spaceship starting at Earth (to cancel out at least part of Earth's orbital speed about the Sun) to do that. Yes, that's a valid point.
the_pwner224 7y ago
With some more detail on the mechanics: Here's a screenshot of an orbit in Kerbal Space Program, an excellent NASA-simulator game (you have a spaceport and make + fly rockets and do science): https://wiki.kerbalspaceprogram.com/wiki/File:KerbalEccentricity.jpg https://wiki.kerbalspaceprogram.com/wiki/File:KerbalEccentri... On the blue orbit, you can see Ap and Pe. Ap is the apogee; the place in the orbit where the spacecraft is closest to the earth. Pe is the perigee, the place where the spacecraft is farthest from the earth. Since the blue orbit is mostly circular, they are at about the same altitude. If you look at the large white orbit, the apogee would be the leftmost point, close to the apogee of the blue orbit. The perigee would be all the way at the right of the image. When your spacecraft is at position X, thrusting your engines will not meaningfully change your current position - the acceleration they generate is negligible to the speed at which you are moving. However, the maneuver will change your speed, which affects your orbit. At the apogee, if you thrust in the direction you are moving, your perigee will increase - the orbit will become even more eccentric. Example: at the apogee you are moving at 100 miles per second. Thrusting the engines will not change your current position much; your current position is determined by your 100 miles per second speed and where you came from. But the maneuver will change your speed to 105 miles per second, which will cause your perigee to become much farther away from the earth. However your apogee will stay in the exact same position. Why? Because in orbit you are basically flying sideways while gravity pulls you down. In a circular orbit this balances out into you flying around in a circle. But if you go faster, you're going more sideways while gravity pulls the same amount. So your orbit becomes more elongated. You can thrust in the direction of movement at any point in orbit, and it will increase the altitude of the orbit on the opposite side of where you are at - if you thrust at apogee the perigee altitude increases, and in the white elongated orbit if you thrust between the apogee and perigee your orbit will become more circular and bigger. Similarly to make an eccentric orbit circular, you get to the apogee and then use the engines to slow down, which brings down the perigee. Since thrusting changes your position on the opposite side of the orbit, the most efficient way to increase your perigee is to thrust while at the apogee. The NASA thing is basically going into an elongated orbit between the Sun and Jupiter, coming back to the apogee near the Sun, and then thrusting. The difference in efficiency between thrusting at the apogee of an orbit and just thrusting in a straight line out into space is really huge. Though I'm not sure why the extra gravity of the Sun makes the maneuver more efficient. If you're interested in this you should definitely play KSP. It's a great game and gives you a great intuitive sense of how these things work.
p1mrx 7y ago
The Oberth effect is interesting. You want to get as low/fast as possible (converting your fuel's gravitational potential energy into kinetic energy), and then do a burn to harvest that energy, dropping the exhaust into the sun while the spacecraft zips away at high speed. It's basically the "tennis ball on a basketball" trick, with rockets.
mabbo 7y ago
No matter how it's explained to me, the Oberth effect still seems like magic, or at least some kind of physics violation. Somehow, we use the same delta-V to get more delta-V.
- greglindahl 7y ago
  You're adding less energy to the exhaust and more to the rocket. The Wikipedia article is a pretty good explanation.
rbanffy 7y ago
> main challenge is solar shielding.. If you carry a solar sail to add a little more push from the Sun's radiation you can spare a little material to build a shade on the other side of the sail.

neom 7y ago

I'm no astrophysicist, but I presume the photo would be of the past? Anyone good at math able to say how far in the past a photo would be?

Sharlin 7y ago
Well, assuming the probe is even going to carry an imager of any sort. Not much to photograph at 1000 AU. Anyway, 1000 AU equals about 138 light-hours, or 5.7 light-days, so that's how long sunlight would have taken to reach the probe at that distance.
deleted 7y ago
[deleted]
tobylane 7y ago
5.7 days https://www.wolframalpha.com/input/?i=1000+au+in+light+days https://www.wolframalpha.com/input/?i=1000+au+in+light+days
mikeash 7y ago
All photos are of the past.

SiempreViernes 7y ago

Well, that ain't gettin built save for a random political blessing by a young dynasty. Something going the very fastest you can go makes a poor platform for close study of planets, and going very far away negates the great advantage of heliophysics: the sun is right there. You could get all their motivational science, except maybe the exoplanet calibration, done with a slower more modest project. Frankly, if your space experiment has resorted to invoking "inspiring humanity to fight the climate crisis", you can just as well drop the science pretense and fish for money from the astrology community.

themgt 7y ago

The proposal sounds technically interesting, but there seems to be growing skepticism of SLS even within NASA. Everyone from Blue Origin, Arianespace/ESA, China etc are working on reusable rockets while SLS is over budget, behind schedule and looks like it may be effectively obsolete before it's even launching payloads (much less by the time (2025?) NASA can actually procure new "RS-25E" engines rather than using its handful of shuttle leftovers) The most exciting near-future space tech to me is SpaceX's goal to achieve in-orbit refueling with Starship. With their much cheaper reusable launches, you could plausibly put a Starship with payload in low orbit, launch 3-4 tankers to fully refuel it and then blast off to anywhere in or out of the solar system faster than anything now remotely conceivable. You could do a mission like this without the complex gravity assists. SLS is a massive pork program and going to be hard to shut down, but as soon as "BFR"/New Glenn are operational I think it's time to start looking at getting NASA out of the rocket business and focused on cool space/science missions.

CptFribble 7y ago
SpaceX has proven that the economics are finally there for private launching. The government should put all the SLS money into the science and extreme boundary-pushing tech research NASA's doing that the economics aren't there for: protections/psych research for long-term space habitation, space farms, probes to the next set of targets (Europa, Titan, interesting asteroids), solar-system scale communications, and orbital manufacturing. NASA laid the groundwork for a larger group of organizations to build on in the earth-to-orbit space. Now NASA should be laying the groundwork for a larger group of organizations to build on in the orbit-to-solar-system space.
rbanffy 7y ago
> launch 3-4 tankers to fully refuel it You could also use the tankers to add propellant (not necessarily fuel) to an NTR or an electric thruster with higher Isp than their methalox engines. A couple decades of low thrust would be pretty good.

ta1234567890 7y ago

It's great to see so much interest in space exploration. However, we should put more effort into exploring our own planet. We've literally only scratched the surface. I bet that if we spent even half as much money as we spend on space programs, trying to get to Earth's core, we would advance science and technology a lot faster. Also, we would have a way better idea of how the magnetic field works and how to harness it - maybe we'd even figure out how to have global wireless communication and gps just with underground technology (no satellites needed). It's as if we are traveling across the universe on this amazing organic spaceship (Earth), but we are on the outside. We should figure out what's inside and how to get there.

whatshisface 7y ago
Space is pragmatic and cost-effective compared to traveling to the Earth's core.
- ta1234567890 7y ago
  Maybe now, but it wasn't when people first decided to do it. Also, it might not be now. If we are able to reliably extract energy from lava/volcanoes, we would have enough energy to power the whole world cleanly, which could help immensely with our current climate crisis. Space is a huge expense of energy, which also contributes to the climate crisis. Free/super-cheap global energy sounds like a huge return on investment.
  - mikeash 7y ago
    Space is a negligible amount of energy. Absolutely tiny. I’d wager that GPS alone has made space a net energy positive by saving energy with better routing.
greglindahl 7y ago
People can do more than one thing at once. We spend a lot of money studying the Earth, from space and the surface. Studying other planets helps understand things about the Earth that would be difficult to figure out by only studying the Earth. Studying other stars helps us understand the Sun. In another comment you say: > If we are able to reliably extract energy from lava/volcanoes, That's already being done at scale, especially in Iceland.

credit_guy 7y ago

"Interstellar Probe, a mission concept for NASA, aims to travel 93 billion miles past the sun" Comparison to other astronomical distances: * 93 BN miles = 1000 AU (AU = astronomical unit = distance from Sun to Earth) * mean distances from Sun to Neptune and Pluto are roughly 30 AU and 40 AU * current distance from Sun for Voyager 1 and 2: 146 AU and 121 AU (see [1] which is quite cool, these distances are updated real time) * 1000 AU = 1.6% of a light year * 1000 AU = 0.36% of the distance to the closest star Alpha Centauri [1]https://voyager.jpl.nasa.gov/mission/status/ https://voyager.jpl.nasa.gov/mission/status/

aruggirello 7y ago

So if this probe is bound to venture into the distance range useful for a solar gravitational lensing telescope, why not use it to deploy one? That would really be a major breakthrough IMHO. https://arxiv.org/abs/1604.06351 https://arxiv.org/abs/1604.06351 "The minimum distance for a solar lensing telescope is 547 astronomical units (AU). And in reality, proper positioning would likely require the telescope to be placed even farther out — perhaps as far as 2,000 AU or more."

rbanffy 7y ago

I always wonder what would be the fastest spacecraft we could build for a given mass budget. NASA should host a competition for designs that could reach one light day/month/year in the shortest time under a given mass constraint using existing or reasonably extrapolated technology.