Interstellar Probe, a Mission Concept for NASA
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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.
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.
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.
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.
[0] - 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
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.
It's basically the "tennis ball on a basketball" trick, with rockets.
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.
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: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.
I don't understand this. If your peri(something), which is by definition less than your apo(something), increases, then isn't your orbit becoming more circular and less eccentric?
In the screenshot, the "active" blue orbit is nearly circular, so the Ap and Pe are similar and the eccentricity is small. Both grey orbits have a higher eccentricity with the periapsis being closest to the body (Kerbin) and the apoapsis being the most distant point, though neither are marked in the screenshot as they're not the actively selected orbit.
I find "apoapsis" easy to remember due to it's similarity to the Latin "apex" [0].
Apoapsis: The point of a body's elliptical orbit about the system's centre of mass where the distance between the body and the centre of mass is at its maximum. [1]
Periapsis: The point of a body's elliptical orbit about the system's centre of mass where the distance between the body and the centre of mass is at its minimum. [2]
[0] https://en.wiktionary.org/wiki/apex#Latin
Too late to edit it now though...
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.
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
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.
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.
I’d wager that GPS alone has made space a net energy positive by saving energy with better routing.
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.
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."
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.