
Interstellar Probe, a Mission Concept for NASA - CrankyBear
https://www.washingtonpost.com/science/interstellar-probe-a-mission-concept-for-nasa-aims-to-travel-93-billion-miles-past-the-sun/2019/07/11/e9b92f5c-92a8-11e9-aadb-74e6b2b46f6a_story.html
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themgt
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
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.

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xt00
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..

~~~
the_pwner224
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:KerbalEccentri...](https://wiki.kerbalspaceprogram.com/wiki/File:KerbalEccentricity.jpg)

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.

~~~
perl4ever
"At the apogee, if you thrust in the direction you are moving, your perigee
will increase - the orbit will become even more eccentric."

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?

~~~
the_pwner224
It's the opposite - apogee is the point closest to the center of orbit,
perigee is the farthest point.

~~~
accrual
Apogee is the point furthest away in an orbit from the center of mass in
relation to the Earth, perigee is the closest point.

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](https://en.wiktionary.org/wiki/apex#Latin)

[1]
[https://en.wiktionary.org/wiki/apoapsis#Noun](https://en.wiktionary.org/wiki/apoapsis#Noun)

[2]
[https://en.wiktionary.org/wiki/periapsis#Noun](https://en.wiktionary.org/wiki/periapsis#Noun)

~~~
the_pwner224
Ah, looks like I got that all backwards. Been a few years since I last played
KSP :)

Too late to edit it now though...

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SiempreViernes
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.

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credit_guy
"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/)

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ta1234567890
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
Space is pragmatic and cost-effective compared to traveling to the Earth's
core.

~~~
ta1234567890
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
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.

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aruggirello
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."

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rbanffy
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.

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neom
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
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.

