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Cubesats for Solar System Exploration
vjkane
post Aug 8 2020, 05:14 PM
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[ADMIN NOTE: New topic started using moved posts from Pallas telescopic observation topic. Please read and keep rule 1.9 in mind. Thanks!]


I was hoping that NASA would select the Athena mission to do a flyby of Pallas using a cubesat spacecraft under the SIMPLEx program. It selected the Janus mission to flyby two near Earth asteroid binary systems instead. The Athena team plans to submit again.


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antipode
post Aug 9 2020, 12:14 AM
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That's good news vjkane! Cubesats for initial exploration of interesting NEOs and objects out to the main belt seem like a great way to go.
I think there's a need for an ongoing program that sits well under the Discovery class cost-wise that can take advantage of cubesat architectures with limited but focused payloads,
only solar power, and new cheaper smallsat launchers or rideshare opportunities.

P
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vjkane
post Aug 9 2020, 01:15 AM
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QUOTE (antipode @ Aug 8 2020, 05:14 PM) *
That's good news vjkane! Cubesats for initial exploration of interesting NEOs and objects out to the main belt seem like a great way to go.
I think there's a need for an ongoing program that sits well under the Discovery class cost-wise that can take advantage of cubesat architectures with limited but focused payloads,
only solar power, and new cheaper smallsat launchers or rideshare opportunities.

P

Don't get too excited. While it was ranked Category 1 (fully selectable on science and implementation), NASA didn't select it. There also has to be a launch opportunity. The previous proposal made use of the Psyche Mars flyby and the fact that Pallas is currently close to the ecliptic.

All we know about the new proposal, based on the PI's statements, is that the next version will be much better.


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JRehling
post Aug 9 2020, 07:51 PM
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Given the low mass of cubesats, I wonder about a mission that sends many of them on a Jupiter (or, possibly, Earth) flyby and spreads them out enough, before the flyby, for the gravity assist to scatter them into solar orbits that cross back through the asteroid belt and fly by many different targets from an initially-similar trajectory. There have to be many opportunities for such orbits to intersect the orbits of two targets (out of thousands to choose from) so that the number of asteroids observed could be on the order of 1.5 per cubesat. Thereby, one low-mass mission could give us flyby observations of many asteroids.

The investment in delta-v for the Jupiter flyby would be high if you only wanted to observe a single target, but for the payoff of observing many targets, the science / cost would become more appealing.

The devil is in the details as to what a Jupiter gravity assist can achieve, but a couple of inspiring examples are Pioneer 11, which gained a high inclination en route to its Saturn flyby, Ulysses, which gained a 79° inclination for observing the Sun. Getting to Pallas is easy in comparison to either of those.
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vjkane
post Aug 10 2020, 01:51 PM
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QUOTE (JRehling @ Aug 9 2020, 11:51 AM) *
Given the low mass of cubesats, I wonder about a mission that sends many of them on a Jupiter (or, possibly, Earth) flyby and spreads them out enough, before the flyby, for the gravity assist to scatter them into solar orbits that cross back through the asteroid belt and fly by many different targets from an initially-similar trajectory. There have to be many opportunities for such orbits to intersect the orbits of two targets (out of thousands to choose from) so that the number of asteroids observed could be on the order of 1.5 per cubesat. Thereby, one low-mass mission could give us flyby observations of many asteroids.

The investment in delta-v for the Jupiter flyby would be high if you only wanted to observe a single target, but for the payoff of observing many targets, the science / cost would become more appealing.

The devil is in the details as to what a Jupiter gravity assist can achieve, but a couple of inspiring examples are Pioneer 11, which gained a high inclination en route to its Saturn flyby, Ulysses, which gained a 79° inclination for observing the Sun. Getting to Pallas is easy in comparison to either of those.

That's almost certainly ballastically possible. Two issues: 1) cubesats still have low reliability and therefore lifetimes and 2) no one has figured out how to as dramatically cut the mission operations costs.


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HSchirmer
post Aug 18 2020, 07:44 PM
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QUOTE (JRehling @ Aug 9 2020, 07:51 PM) *
Given the low mass of cubesats, I wonder about a mission that sends many of them on a Jupiter (or, possibly, Earth) flyby and spreads them out enough, before the flyby, for the gravity assist to scatter them into solar orbits that cross back through the asteroid belt

It occurred to me that it might make sense to reverse direction first - Venus is closer and IIRC aligns more often for flybys(?) So an initial Venus gravity/Oberth boost might be a faster way to get out to Jupiter. Also, I VAGUELY remember that rockets using RP1 for fuel (kerosene/diesel) are denser, and pack more delta-v for Oberth maneuvers boosts, compared to cryogenics (H2 or CH4) or hypergolics. IIRC problem is, if you fly RP1 past ~1.0 AU it turns into Jello unless you heat and stir it. So, perhaps aim IN towards Venus, use cheap Lox-RP1 and get the Oberth/gravity boost there?

Also seems to me that a cubesat heading towards the asteroid belt could benefit from some sort of solar sail, for course correction on the way out, for station keeping once you get there, and as a solar collector to reflect light back onto the cubesat solar cells to keep the battery charged and the cubesat alive.

Question- how much of an Oberth/gravity boost CAN you get from a sling shot maneuver around the moon?
I have to ask, because years ago, somebody speculated that the GRAIL data and a super accurate lunar gravity map would allow a bonkers "Tors Twillinger"-"REVERSE HOVER-SLAM" massive Oberth & gravity boost from a lunar flyby.
It's essentially the "Thor's Twins" turn from The-Hunt-For-Red-October, (but with a rocket.)
You skim over the surface of the moon around 300 feet/100 meters above the surface, now that you are deep in the Lunar gravity well you light up a high delta-v Lox-RP1 engine, blast across the lunar seas, and then thread the gap through the mountains at the west end of the Ocean of Storms, then make the final course correction that gets you to the outer solar system in a hurry.
Could it work?
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antipode
post Aug 18 2020, 10:34 PM
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You don't want to mix up your metric and imperial units for THAT one! cool.gif

P
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stevesliva
post Aug 19 2020, 02:33 AM
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QUOTE (antipode @ Aug 18 2020, 05:34 PM) *
You don't want to mix up your metric and imperial units for THAT one! cool.gif


(re: Star Wars lunar gravity boost)

Right, you instead mix up whether you're using units of distance or units of time. laugh.gif
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HSchirmer
post Aug 19 2020, 02:40 AM
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QUOTE (antipode @ Aug 18 2020, 11:34 PM) *
You don't want to mix up your metric and imperial units for THAT one! cool.gif
P

Ah, the "good old days." Friday, April 20, 1962. Neil Amstrong bounced an X-15 off the atmosphere, then executed the fastest U-turn in human history, and came in low and fast into Rosamond dry lake.

-"Tower, AirBoss wants to know, just how far WAS Neil from the Joshua trees?"
- Capcom Petersen "Um, tell AirBoss, that, eh, Neil was AT LEAST 150 feet away from the Joshua trees."
- "This is AirBoss to Tower. Were those trees on Neil's right or his left..."
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JRehling
post Aug 19 2020, 09:55 PM
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1) Venus does not align more often for flybys; this is easy to lookup and check. The synodic period of Venus is 19 months and for Jupiter, 13 months… not that the difference would matter much in planning a single mission.

2) Adding a solar reflector for two purposes to each cubesat immediately defeats the principle of simplicity. I was suggesting that there might be an affordable, elegant solution and you're proposing an expensive solution; of course, those always exist. That's just an entirely different topic.

3) The magnitude of possible gravity assists depends upon many factors, but they vary with the amount of time that the spacecraft spends within the body's gravity well… time integrated times the acceleration due to gravity at that distance… and Jupiter has a mass 390 times that of Venus. It has easily the greater potential for bending the paths of objects on similar trajectories to different destinations.
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HSchirmer
post Aug 20 2020, 03:45 AM
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QUOTE (JRehling @ Aug 19 2020, 10:55 PM) *
2) Adding a solar reflector for two purposes to each cubesat immediately defeats the principle of simplicity. I was suggesting that there might be an affordable, elegant solution and you're proposing an expensive solution; of course, those always exist. That's just an entirely different topic.

Fair points. My points
1) cubesats rely on batteries & solar panels, not plutonium RTGs.
2) A big shiny flat solar sail would allow a cubesat to make course corrections without needing heavy cold gas thrusters.
3) The same big shiny sail, when parabolically curved, would focus dim sunlight onto a cubesat solar panel, allowing a cubesat to survive on solar power much further out that it could otherwise.
QUOTE
and Jupiter has a mass 390 times that of Venus. It has easily the greater potential for bending the paths of objects on similar trajectories to different destinations.

4) Of course, the sun has a mass 333,000 times that of Venus, is only 1 AU away and has NO synodic period, so it's thousands of times better for bending orbital paths.
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HSchirmer
post Aug 20 2020, 06:04 PM
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Looks like the cubesat-solar sail is now in the extended mission...

https://spacenews.com/solar-sail-spacecraft...tended-mission/

The next size up seems to be CubeSail, designed by CU Aerospace (Champaign-Urbana Aerospace) and the University of Illinois, is a low-cost flight experiment based on the UltraSail concept. This experiment uses two CubeSat satellites to deploy a 20 sq. meter solar sail, which can play the same role as propellant on a conventional spacecraft.
https://www.cubesail.us/
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JRehling
post Aug 21 2020, 01:43 AM
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There are multiple reasons why the Sun is not an easy object for gravity assists.

Most compelling for the reason at hand, the Sun is not close in terms of delta-v; it is actually the single object in the universe that requires the most delta-v to reach. It is much less delta-v to reach Jupiter.
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HSchirmer
post Aug 21 2020, 02:59 AM
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QUOTE (JRehling @ Aug 21 2020, 02:43 AM) *
There are multiple reasons why the Sun is not an easy object for gravity assists.

Most compelling for the reason at hand, the Sun is not close in terms of delta-v; it is actually the single object in the universe that requires the most delta-v to reach. It is much less delta-v to reach Jupiter.


Excellent points, as usual.

Here's a quick run from the excellent "Atomic Rockets" website...
http://www.projectrho.com/public_html/rock...on.php#oberthe0
QUOTE
The Sun increases the speed of the spacecraft during its run towards the solar surface, so that our ship, at rest far from Sol, will be moving at 600 kms/second as it sweeps past the solar photosphere. The kinetic energy of a body with velocity V is V2/2 per unit mass, so for an object moving at 600 kms/second, a 10 kms/second velocity boost increases the kinetic energy per unit mass by (6102-6002)/2 = 6,050 units. If the same velocity boost had been used to change the speed from 0 to 10 kms/second, the change in kinetic energy per unit mass would have been only 50 units. Thus by applying our speed boost at the right moment, when the velocity is already high, we increase the energy change by a factor of 6,050/50 = 121, which is equivalent to a factor of 11 (the square root of 121) in final speed. Our 10 kms/second boost has been transformed to a 110 kms/second boost.

All that the Sun has done to the spaceship is to change the speed relative to the Sun at which the velocity boost is applied. The fact that kinetic energy goes as the square of velocity does the rest.
...
The gain in speed is maximum if you fall in with zero velocity from a long way away. In the case of Sol, the biggest boost you can obtain from your 10 kms/second velocity kick is an extra 100 kms/second.


Fastest rocket yet was New Horizons using an Atlas/Centaur at 16km/s.
(For comparison, the Falcon Heavy tossed a Tesla at Mars at around 12km/s.)
So, an solar Oberth effect maneuver by an Atlas/Centaur should net ~10x that, about 160km/s.
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Holder of the Tw...
post Aug 21 2020, 03:07 PM
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QUOTE (JRehling @ Aug 20 2020, 08:43 PM) *
... the Sun is not close in terms of delta-v; ... It is much less delta-v to reach Jupiter.


Yes, that's true in terms of going there directly. In a different sense though, it's the same delta-v as Jupiter, provided you go to Jupiter first. You can use Jupiter's gravity to slingshot a probe arbitrarily close to the sun. So if you are willing to add several years to the journey plus some hefty radiation hardening for Jupiter's environment, you can pull off getting to the sun with a lot less energy.

In early designs for the Parker probe, a Jupiter assist was being seriously considered. The result would have been a probe that could reach a point three times closer to the sun than it is in fact going to (pretty much the minimum survivable distance with current technology). All at the expense of spending very little time at the sun.

Here is an article at the Parker website that discusses that option:Change in Mission Design
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