How Does Rosetta Maintain Its Position Relative to the Comet?

  • Context: Undergrad 
  • Thread starter Thread starter docroc
  • Start date Start date
  • Tags Tags
    Orbit Orbits
Click For Summary

Discussion Overview

The discussion revolves around the mechanics of how the Rosetta spacecraft maintains its position relative to the comet, particularly focusing on the gravitational effects of the comet and the nature of its orbit. Participants explore concepts related to orbital dynamics, energy requirements for maintaining orbits, and the implications of the comet's low gravity.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • Some participants question whether Rosetta is truly orbiting the comet or simply moving alongside it in a straight line due to the comet's negligible gravity.
  • Others clarify that Rosetta is indeed in orbit around the comet, adjusting its trajectory using thrusters and varying its orbit for scientific purposes.
  • One participant estimates the orbital speeds of Rosetta and discusses the implications of these speeds on its orbital period.
  • Another participant notes that the comet's low gravity allows Rosetta to travel in an unbound path with minimal delta-V requirements.
  • There is a discussion about the relationship between gravitational force, orbital speed, and radius, suggesting that there is always a velocity that can allow for an orbit, regardless of the mass of the central body.
  • Some participants express confusion about how orbiting works with such low gravitational fields compared to larger bodies like Earth.

Areas of Agreement / Disagreement

Participants generally agree that Rosetta is in orbit around the comet, but there are varying interpretations of how this is achieved given the comet's low gravity. The discussion includes both agreement on certain principles of orbital mechanics and ongoing questions about the specifics of Rosetta's motion.

Contextual Notes

Participants express uncertainty regarding the exact mechanics of Rosetta's orbit, particularly in relation to the comet's gravitational influence and the energy required for maintaining its position. Some assumptions about orbital dynamics and the nature of gravitational forces are not fully resolved.

docroc
Messages
9
Reaction score
0
News stories make it sound like Rosetta is orbiting the comet. But presumably the comet's gravity is negligible, which means that orbiting it would require continuous acceleration (and therefore continuous use of energy) in order for Rosetta's motion to conform to a circle/ellipse, rather than simply moving in a straight line as it would naturally do without any input of energy.

Is Rosetta in fact simply moving alongside the comet in a straight line? Or am I missing something?

(Afterthought 5 mins later) Is Rosetta matching the comet's orbit around the sun?
 
Last edited:
Astronomy news on Phys.org
I'm not sure if you heard yet, but it already landed.
 
docroc said:
News stories make it sound like Rosetta is orbiting the comet. But presumably the comet's gravity is negligible, which means that orbiting it would require continuous acceleration (and therefore continuous use of energy) in order for Rosetta's motion to conform to a circle/ellipse, rather than simply moving in a straight line as it would naturally do without any input of energy.

Is Rosetta in fact simply moving alongside the comet in a straight line? Or am I missing something?

(Afterthought 5 mins later) Is Rosetta matching the comet's orbit around the sun?
Rosetta is in orbit around the comet. It has changed its orbit from time to time by firing thrusters. But a lot of the time it just loops around and around.

I estimate orbit speeds to be on the order of 10 cm per second, but when closer in can be. say 20 cm per second, depending on the orbit radius, which the controllers have varied in order to study the surface and release the lander and communicate with the lander etc etc.

Just as a sample calculation how far can you travel in one Earth day (86,400 seconds) at 20 cm/s?
17 kilometers
So mightn't Rosetta sometimes complete an orbit in 2 Earth days?.

Maybe now she has retired to a farther out orbit because the work of the moment has been done, the lander is inactive so doesn't have to be communicated with, and so on. I don't know anything about the current status.
 
Last edited:
The comet's gravity is low enough so that Rosetta can easily travel in an unbound path without needing much delta-V.

A surface satellite on the comet would travel at something like 0.7 m/s, though the comet's highly irregular shape makes it difficult for there to be such a satellite.
 
Mr.CROWLER said:
I'm not sure if you heard yet, but it already landed.
The probe landed, but Rosetta (the mother ship) is up there watching.
 
lpetrich said:
The comet's gravity is low enough so that Rosetta can easily travel in an unbound path without needing much delta-V.

A surface satellite on the comet would travel at something like 0.7 m/s, though the comet's highly irregular shape makes it difficult for there to be such a satellite.
I'm still confused - maybe my question wasn't clear about what I don't get.

With a satellite orbiting earth, I understand that the Earth's gravitation keeps the satellite in orbit rather than flying off in a tangent to the orbit (?) and this requires a velocity of around 25k miles/hr for the satellite. So, with almost no gravitational field how does the comet do this for Rosetta? Is it just a question of matching the velocity of Rosetta so that it is appropriate to balance the low gravitation of the comet, ie is there always a velocity that can be used to "match" to any sized object around which you want to orbit?
 
docroc said:
Is it just a question of matching the velocity of Rosetta so that it is appropriate to balance the low gravitation of the comet, ie is there always a velocity that can be used to "match" to any sized object around which you want to orbit?

Yes. The radius of a circular orbit, the orbital speed, and the gravitational force are related by ##F=mv^2/r## so no matter how small ##F## is, there is always some ##v## that will allow an orbit at any given radius. Elliptical orbits are a bit more complicated, but it's the same general idea.
 
Yes. 67P masses 10^13 kg with gravity about 10^-3 m s^-2 or 10^-4 g Earth's gravity.
 
Nugatory said:
Yes. The radius of a circular orbit, the orbital speed, and the gravitational force are related by ##F=mv^2/r## so no matter how small ##F## is, there is always some ##v## that will allow an orbit at any given radius. Elliptical orbits are a bit more complicated, but it's the same general idea.

Thanks for your clear answer,
Dave
 

Similar threads

Undergrad How Does Rosetta Maintain Orbit Around a Low-Gravity Comet?
  • · Replies 7 ·
Replies
7
Views
2K
Undergrad Can a Satellite Maintain its Angular Velocity with Continuous Low Thrust?
  • · Replies 2 ·
Replies
2
Views
2K
Undergrad How Does Mass Influence Spacetime Curvature?
  • · Replies 13 ·
Replies
13
Views
2K
Calculating Min Δv for a Comet to Intersect Earth's Orbit
  • · Replies 4 ·
Replies
4
Views
2K
How Does Comet Speed Change at Aphelion Compared to Perihelion?
  • · Replies 1 ·
Replies
1
Views
4K
Undergrad On gravity and the conservation of energy
  • · Replies 30 ·
2
Replies
30
Views
5K
Studying Skipping Chapters in Stewart’s Calculus? (Pearson's Edexcel IAL Background)
  • · Replies 2 ·
Replies
2
Views
1K
Input/processing aspects of adaptive camouflage
  • · Replies 2 ·
Replies
2
Views
4K
Graduate How does the wave-particle duality of light affect its behavior?
  • · Replies 6 ·
Replies
6
Views
3K
Large Scottish Pumped Storage Hydroelectric Reservoir and Dam (@ Coire Glas)
  • · Replies 20 ·
Replies
20
Views
9K