4
$\begingroup$

Advance our technology 200 years, develop very precise celestial navigation controls and very efficient nuclear reactors. Distill to ensure only the most stable elements are used in production, cost is no issue.

After those parameters are met, I want a receiver to remain in an exact position within the solar system, outside the planetary orbits.

My receiver collects signals from far off and needs to keep a constant velocity exactly equal to that of the sun (according to it's path in the Milky Way). The signal need to be able to reliably know where to aim its antenna, and maintain a steady phase relationship. So the receiver's distance and orientation to the sun must be maintained. The whole system is moving through the galaxy as a unit. That means it can't orbit anything (including the sun).

So I thought of a solar sail which can be vented or skewed to do minor adjustments:

Solar guided receiver

Three components:
1) Detector - Tethered to the receiver 5 microseconds (1,500 meters) closer to the sun. It senses solar flux changes 1.875 ms before they hit the receiver.

2) Receiver - provides power and guidance. The receiving antenna is articulated to absorb any vibrations and to make fine tuning adjustments while the body makes corrections. It also controls the sail via sail lines, to increase or decrease the surface area, as well as steer it. For abrupt surges (solar wind gusts) it can also "pay out" line to avoid a jolt, reduce the sail area, then retract the sail. It has 1.875 mS to plan for this.

3) Sail - Collects solar winds for propulsion and stabilization. It can vary surface area and be skewed for steering.

The detector senses then warns the receiver in advance of incoming changes in solar flux. It is tethered to the receiver, sending correction signals by laser, which is quite far away (5 microseconds). I'm assuming winds of 800 km/s

This is receiving a signal from a deep space relay, so no communication happens. It can measure input signal drift and will automatically correct for that however. So if the signal starts fading "left" it knows to adjust the antenna right. It also must maintain the phase relationship with the transmitter (no erratic or abrupt changes). Otherwise, it needs to stay put. It has nuclear powered electricity generation and a solar charger.

In 200 years can something like this exist to keep an antenna perfectly stationary with the sun?

(In other words, the receiver and the sun travel along the exact same vector in the galaxy at a constant distance from eachother).

Improve this question
$\endgroup$
7
  • $\begingroup$ "needs to keep a constant velocity exactly equal to that of the sun" -- the Sun's velocity relative to what? This is a very important part of your question. $\endgroup$
    – Roger
    Oct 31, 2019 at 19:31
  • 1
    $\begingroup$ Why? It's a parameter. If it's not met, the plot fails. The "why" is not relevant to a question of "can it be done." It's like trying to attack a premise that doesn't exist. $\endgroup$
    – Vogon Poet
    Oct 31, 2019 at 19:35
  • 1
    $\begingroup$ Oh I see your question... relative to the sun's direction of travel. Our system has what's called a "heliopause" which is slightly different at the front of the travel. So relative to the direction of travel in the galaxy. $\endgroup$
    – Vogon Poet
    Oct 31, 2019 at 19:43
  • $\begingroup$ You may be interested in the galactic coordinate system. If I am understanding the question correctly, you can state that the receiver is at a fixed point in the galactic coordinate system as defined by IAU. Still doesn't get around the frame challenge by Morris the Cat (this is still the hardest way to accomplish your goals, not the easiest), but using a IAU standard would remove all ambiguity. $\endgroup$
    – Cort Ammon
    Oct 31, 2019 at 21:16
  • $\begingroup$ Good reference, assuming it still exists then. Constant vector is going to be the easiest to synchronize in any case. I get some people make assumptions that could change that. $\endgroup$
    – Vogon Poet
    Oct 31, 2019 at 22:08

4 Answers 4

Reset to default
1
$\begingroup$

Robert l Forward invented this back in the 1980's as a "Statite". Forward realized that a light enough sail could balance the acceleration from the Sun's light against the Sun's gravitational pull, and essentially have the Statite remain fixed in place.

enter image description here

Statite hovering over the Earth

The ultimate version of this idea would be to create a "Dyson shell" of Statites hovering around the Sun collecting solar energy and powering a vast solar civilization. The estimated mass would be similar to that of a large asteroid, converted into molecule thin solar sails and a delicate web of tethers holding their payloads against the Sun's acceleration and gravity.

enter image description here

Fanciful depiction of a Dyson buble

A statite deployed around our own sun would have to have an overall density of 0.78 grams per square meter of sail. The total mass of a bubble of such material 1 AU in radius would be about 2.17 × 10^20 kg, which is about the same mass as the asteroid Pallas.

Improve this answer
$\endgroup$
7
$\begingroup$

My receiver collects signals from far off and needs to keep a constant velocity exactly equal to that of the sun. The signal need to be able to reliably know where to aim its antenna,

so the receiver's distance and orientation to the sun must be maintained. That means it can't orbit anything.

I'm going to make a frame challenge here, because this problem does not require this solution. Adjusting for changing orbital position to allow your receiver to stay pointed directly at its target is a computationally trivial exercise, observatories on Earth do it all the time, and certainly it would be VASTLY easier to put your receiver in a stable orbital position and have it adjust its focus to track the target than it would to try and actually keep it fixed to the star in the way you're suggesting. At the very least it would require vastly more energy to have it NOT orbit the sun than it would to have it orbit and adjust accordingly, and the further away your target is, the easier it becomes.

Improve this answer
$\endgroup$
7
  • 1
    $\begingroup$ But you are constantly varying the distance to the signal, making drastic phase changes. The signal cannot deviate - or not erratically so, it's not a simple 2D alignment issue. Its a 3D alignment solution. I said what I said because it needed to be said."the receiver's distance and orientation to the sun must be maintained" Orbits are not a solution. $\endgroup$
    – Vogon Poet
    Oct 31, 2019 at 18:55
  • 5
    $\begingroup$ @VogonPoet Again, this is REALLY easy to solve and adjust for computationally. Any variation that's this predictable is trivially easy math problem. $\endgroup$
    – Morris The Cat
    Oct 31, 2019 at 19:06
  • 5
    $\begingroup$ Why can't it oscillate? It's going to change slowly over time ANYWAY because the two stars aren't fixed to each other, so your distance is going to shift over time no matter what. If you're adjusting for that, you can adjust for the orbit as well. $\endgroup$
    – Morris The Cat
    Oct 31, 2019 at 19:28
  • 7
    $\begingroup$ @VogonPoet your solar sail arrangement involves unpredictable variation due to solar flux that you have to constantly track and adjust for, where the orbital period is predictable to dozens of decimal places over millenia. There's no math that makes that risk assessment make sense. $\endgroup$
    – Morris The Cat
    Oct 31, 2019 at 19:34
  • 1
    $\begingroup$ Phased arrays accounting for Doppler shift due to changing distances for transmission and reception are a solved problem. $\endgroup$
    – Keith Morrison
    Nov 4, 2019 at 5:40
5
$\begingroup$

Sure.

Okay, so you've got the Sun sitting there, and it has some sort of velocity vector V, with respect to... something -- like the center of the Milky Way galaxy.

And you've got your receiver sitting out there, and it also has velocity vector V, and furthermore it's at D distance from the Sun.

Can the receiver stay that way? Sure.

It is subject to various accelerating forces, with respect to the Sun, that we can add up into a vector A. There's the gravitational force of the Sun, and to (much) lesser extents, gravitational forces from the planets, solar wind pressure, etc.

The receiver just needs to exert an equal force in the direction opposite to A. No net force, no acceleration, things stay the way they are. Since it can tell if it's wandering off-beam, it can figure out what it needs to do to correct for that.

To exert this force, it'll need some method of generating thrust. Ion thrusters would probably be good. Cost is no object, so send up as much propellant as you feel like. And/or send out refuelling craft. Or just replace the whole thing on a regular basis; you'll probably want a fleet for redundancy anyway.

Improve this answer
$\endgroup$
3
  • 1
    $\begingroup$ You are using fueled ion thrusters instead of the sail, or to aid it? This answer never mentioned if the sail did anything at all. My research suggests solar winds can negate at least the sun's gravity with a large enough sail. $\endgroup$
    – Vogon Poet
    Oct 31, 2019 at 20:23
  • $\begingroup$ In my opinion the sail is a bad idea -- cumbersome and finnicky and out around the Oort Cloud you're just not getting much thrust out of it. Particularly for attitude control it would be a pain in the butt. I (or someone) could crunch the numbers for you as to just how much thrust per square kilometer you could get, but if your story can withstand the violence, I'd just get rid of it. $\endgroup$
    – Roger
    Oct 31, 2019 at 20:27
  • 2
    $\begingroup$ TViolence? And why would I be in the Oort Cloud? There’s millions of miles of space after Pluto before terminal shock, lots of wind in there! Winds are probably even stable. $\endgroup$
    – Vogon Poet
    Oct 31, 2019 at 22:10
1
$\begingroup$

One main problem with sail

The main problem with a solar sail is the size it would need to be. You have stated that money and resources are no object, but the following problems arise:

  • Can the tether be strong enough to carry the receiver?
  • Is there enough surface area on the receiver for the tether?

For example if you have a few carbon nanotube fibers tethering the sail to the receiver, it likely won't be strong enough. It is possible that the amount of fibers you'd need would be so great that you won't have enough space for them all.

This was my previous answer:

This is not possible (not in the way you're asking)

Unfortunately, the rotational period of stars is differential. That means that the rotation at the equator of a star is often faster than the rotation at the poles.

If you are only looking to stay stationed related to the rotation at the equator, you may do so by placing the receiver in a heliostationary orbit. This would require much less power and resources than trying to maintain a non-orbital point of reference around the sun.

The receiver is able to compute exactly what forces are necessary to keep itself positioned in the way that is desired, and then execute appropriate maneuvers.

Improve this answer
$\endgroup$
7
  • $\begingroup$ This sounds like two contradictory answers. Does it "require much power and resources" or is it "impossible?" You have both in here? Again this is 200 years ahead, we have a power source however a solar sail does the bulk of the stabilization work. Q: "How big?" A: "Big enough." $\endgroup$
    – Vogon Poet
    Oct 31, 2019 at 19:12
  • $\begingroup$ And why does a vehicle propelled by a solar sail care about the sun's rotational period? I imagine flux rates will vary, but I've compensated for that. $\endgroup$
    – Vogon Poet
    Oct 31, 2019 at 19:14
  • $\begingroup$ @VogonPoet I believe you misunderstand what "___stationary" means. Words such as "geostationary" and "solo/heliostationary" are in fact referring to a situation in which an object has an orbital period equal to the more massive object's rotational period. If this is not what you desire, you did not use the right word. $\endgroup$
    – overlord
    Oct 31, 2019 at 19:29
  • $\begingroup$ I think you are referring to a geostationary orbit. That has the word "orbit" as a necessary part of the description. This is not in an orbit, it's gust "heliostationary" (sans "orbit"). But thank you for finding the correct word! I'm correcting my question. (if there is yet a different word for "staying in a parallel vector with the sun" that would also be good) $\endgroup$
    – Vogon Poet
    Oct 31, 2019 at 20:02
  • $\begingroup$ @VogonPoet Are you saying that you don't want the receiver to move around the sun at all? You simply want it to have the same exact velocity and direction as the sun, while avoiding falling into an orbit? $\endgroup$
    – overlord
    Nov 1, 2019 at 14:17

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .