Why use Earth as a gravity assist?

Click For Summary

Discussion Overview

The discussion revolves around the mechanics and reasoning behind using Earth as a gravity assist for missions targeting deep space, particularly in the context of planning a mission to a Jupiter trojan asteroid. Participants explore the efficiency of using Mars for slingshots compared to Earth, considering various factors that influence trajectory planning.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant questions the efficiency of using Earth for gravity assists, suggesting that a Mars slingshot might save time and fuel.
  • Another participant notes that Earth is significantly more massive than Mars, which could influence the effectiveness of a gravity assist.
  • A participant raises the issue of alignment, stating that a Mars flyby requires precise positioning of all three bodies (Earth, Mars, and Jupiter), while an Earth flyby only requires alignment between Earth and Jupiter.
  • Some participants argue that while a Mars slingshot could be more efficient, the infrequency of proper alignments makes it less practical.
  • It is mentioned that velocity changes at perihelion are more effective for increasing aphelion, which may favor Earth as a slingshot target.
  • Another participant adds that Earth's higher velocity relative to the central body also contributes to its suitability as a slingshot compared to Mars.
  • It is highlighted that launching from Earth provides a natural trajectory that simplifies the mission planning process, requiring only minor adjustments for the slingshot maneuver.

Areas of Agreement / Disagreement

Participants express differing views on the practicality and efficiency of using Mars versus Earth for gravity assists. While some acknowledge the advantages of Earth, others propose that Mars could be a viable option under certain conditions, indicating that the discussion remains unresolved.

Contextual Notes

Factors influencing the optimal flight path include mass, velocity, alignment of celestial bodies, and the timing of maneuvers, which are not fully explored in the discussion.

JayFlynn
Messages
7
Reaction score
0
I am doing research for my aerospace engineering dissertation to plan a mission to a Jupiter trojan asteroid. I was researching the type of outgoing trajectories used in missions such as JUNO, Galileo and Europa and noticed they all use Earth as a gravity assist in getting to deep space. Surely be more efficient and save time if a Mars slingshot was used rather than performing deep space manoeuvres way beyond Mars' orbit just to come back to Earth for a slingshot? Can anyone explain the mechanics of why NASA do it like this?
https://upload.wikimedia.org/wikipe...x-Juno's_interplanetary_trajectory_en.svg.png
 
Astronomy news on Phys.org
Earth is 10x more massive than Mars.
 
so why can't you just do a really close slingshot around Mars to make up for it's small mass?
 
With a Mar's flyby you would have to wait until all three bodies were in their proper relative positions to make it work. With an Earth fly-by, only Earth and Jupiter have to have the proper relative positions.
 
  • Like
Likes   Reactions: JayFlynn
So, it would be more efficient to do a Mars slingshot but they're aligned so infrequently that it's not worth waiting?
 
JayFlynn said:
So, it would be more efficient to do a Mars slingshot but they're aligned so infrequently that it's not worth waiting?
I wouldn't go that far. There are a lot of factors that going into determining what the optimal flight path is. For example, not only is Earth 10 times more massive than Mars, velocity changes made when the probe is at or near its perihelion are more effective than those made at other points of its orbit if you are trying to increase the aphelion.
 
Janus said:
I wouldn't go that far. There are a lot of factors that going into determining what the optimal flight path is. For example, not only is Earth 10 times more massive than Mars, velocity changes made when the probe is at or near its perihelion are more effective than those made at other points of its orbit if you are trying to increase the aphelion.

Cheers Janus. This is really helpful!
 
The two things affecting the value of a body for a slingshot are its mass and its velocity relative to the central body. Earth is not only more massive than Mars, but it's moving faster as well. Mars is, generally speaking, not a great slingshot target.
 
Earth is also easy to get to. Any object launched from Earth is automatically on an Earth-crossing trajectory. Giving your spacecraft an eccentric solar orbit with an semi-major axis of 1 AU will return you to Earth in 1 year. Only minor deep space burns are required to fine-tune the slingshot.
 

Similar threads

  • · Replies 19 ·
Replies
19
Views
3K
Replies
1
Views
2K
  • · Replies 86 ·
3
Replies
86
Views
8K
  • · Replies 6 ·
Replies
6
Views
3K
Replies
3
Views
4K
Replies
4
Views
3K
  • · Replies 1 ·
Replies
1
Views
4K
Replies
1
Views
3K
  • · Replies 13 ·
Replies
13
Views
3K
Replies
1
Views
5K