# Tag Info

## Hot answers tagged gravity-assist

64

It's the gravitational attraction of the Sun. Voyager is moving away from the Sun and is pulled back by its gravity. Since Voyager is not moving directly away from the Sun, it's trajectory also curves.

34

Additionally, the probe has just passed a large planetary body with its own gravity well. The probe has to climb up out of that planet's gravity well which costs momentum. There is a net gain in momentum overall, the probe is leaving with more momentum than it entered the slingshot manoever, but the highest velocity is about where the probe is moving ...

14

Before I start my answer: This is not a rockoon anymore, since there is no balloon part. It's just a quirky air launched rocket. My answer: No. What you are doing is: Phase 1: Climb with a plane Phase 2: Descend with a plane Phase 3: Climb without a plane So yes, Phase 3 climb will begin with higher speed. However, since it's all energy that was gained ...

14

Here is a paper which among other things includes the results of a trajectory search. They say Gravity assists of Earth, Venus, and Mars were included with a patched conics assumption. Jupiter was immediately discarded as it is out of phase during the desired time period. The trajectories proposed in that paper involve multiple Earth and Venus flybys. I ...

12

Using Mercury for a slingshot has 3 major problems: Low energy transfer: Mercury is moving relatively quickly but it's low mass means you don't get much benefit You have to slow down to get to it. Mercury is close to the sun, and getting close to the sun means you have to slow your orbit down. Messenger used its Venus and Earth flybys to slow down, not ...

11

Back in 1983 the International Sun-Earth Explorer 3 spacecraft (ISEE-3) was diverted, via a very small ∆V and Earth-moon gravity well manipulations, from its Sun-Earth L1 halo orbit to a rendezvous with comet Giacobini-Zinner in 1985, summarized in this popular article. Also related: Why was ISEE-3 "the most cost-effective spacecraft we ever had" ...

11

@OrganicMarble nailed it: ...it looks like it's the distance from the ecliptic plane. Yep, it's height above/below the ecliptic, a way to represent 3D in a 2D plot. At first I thought they might be thrust vectors like these but no, these are ballistic arcs. Instead I am 99.44% certain that these lines are use to indicate height above/below the plane of the ...

5

In simple terms, gravity pulls an object directly towards another object. As an analogy, if you are running down the street and grab hold of a lamp post with your left hand you will swing around it to the left, if you grab it with your right you will swing to the right. You can use this to do a u-turn, letting go whenever you or going the right direction, or ...

5

Yes. The primary mission of the New Horizons probe was to do a flyby of Pluto in 2015, after which funding was secured to look for an appropriate Kuiper Belt object to target for another flyby. The probe's maneuvering capability was quite small, so it was challenging to find something near enough to its trajectory that it could divert to, but it performed a ...

5

Retrograde thrust at periapsis doesn't lower the periapsis, it lowers the apoapsis. If you're trying to lower the periapsis, you need to apply thrust at apoapsis. If you're trying to lower your periapsis to a point absurdly close to the Sun, the most efficient option that avoids gravity assists is a bi-elliptic transfer: raise your apoapsis as high as ...

4

Just a short supplementary to try and add a more "intuitive" understanding to the two excellent "equation-based" answers. For me the easiest way to think of this is that you have cause and effect reversed in your description of the problem. Consider PSP at aphelion, which is always more or less at Venus distance from the Sun, so that it ...

4

Yes. The THEMIS mission, launched in 2007, was designed as a constellation of five Earth-orbiting satellites in coordinated high earth orbits (with orbital periods of 1 day, 2 days, and 4 days). After the two-year prime mission, the orbits of the two outer probes would have been perturbed away from the regions of scientific interest in the Earth's ...

4

Definitely no. Especially for New Horizons I would say Jupiter gravity sssist was one of "safest" stages of the mission. :) Because New Horizons' closest flyby of Jupiter was rather far - at 2.3 million kilometers. Gravity assists require specific trajectory of flyby - with specific direction and velocity. How precize should they be, how large is ...

3

Launch is usually the most dangerous time for any space mission, especially those that don't land on a celestial body. Historically there is about a 98% chance of successful launch. We've never had any issues that have resulted from a bad flyby, and had a spacecraft cruising around the Jupiter system for extended periods of time, that was never really a ...

3

The New Horizons mission tutorial you refer to may come from our blog here. You'd have to do something similar. Astrogators Guild Blog For multiple flyby missions, Marty Ozimek and Justin Atchinson at APL did a great job of describing a similar problem with multiple flybys here: APL Example

2

If we look to the speed of Voyager 2 relative to Jupiter, this maximum of this speed should occur at perijove. If distance to Jupiter increases after perijove the speed of Voyager in the jovian reference frame would decrease. But the transfer of energy from Jupiter to Voyager by gravity assist is not finished at perijove. If we use the reference frame of the ...

2

In the early years of space exploration, there were a number of accidental solar probes, such as Luna 1 and Ranger 3. Both these missions were intended to hit the Moon; both missed and ended up in solar orbit instead.

2

Another way to express the results of the vis-viva equation at apoapsis is $${v_a}^2 = \frac{2\mu}{r_p+r_a}\frac{r_p}{r_a} = \frac{2\mu}{r_a}\frac{r_p}{r_p+r_a}\tag{1}$$ where $v_a$ is the velocity at apoapsis, $\mu$ is the standard gravitational parameter $\mu\equiv GM$, and $r_a$ and $r_p$ are the apoapsis and periapsis distances. On holding the apoapsis ...

2

When thinking about the speeds and distances in a Keplerian orbit we turn to our friend the vis-viva equation: $$v^2 = GM \left( \frac{2}{r} - \frac{1}{a} \right)$$ where $v$ is the speed at distance $r$ for an object with a semi-major axis $a$ and $GM$ is the gravitational constant $G$ times the Sun's mass M. We can call that product the standard ...

2

As Mark already pointed out: Retrograde thrust at periapsis doesn't lower the periapsis, it lowers the apoapsis. If you're trying to lower the periapsis, you need to apply thrust at apoapsis. This will be very important: every maneuver you plan effects basically the opposite site of your orbit.. want to lower Pericenter? -> retrograd thrust at Apocenter....

2

No, there wouldn't be any way to use Jupiter's gravity as for an assist because the spacecraft is already around orbit around it, or around Callisto which amounts to the same thing. In a gravity assist energy must be exchanged between two gravitational bodies, for example when the Voyager probes got assists the forces acted upon the probes and Jupiter ...

1

You don't start with a departure date--that's one of the answers, not one of the inputs. I don't know a formula for calculating a gravity assist orbit so I will use the easy case and omit Venus, as well as assuming the planets are in circular, coplanar orbits: Find the orbital period of the transfer orbit. For our simple case the orbital radius is (mercury ...

1

When the bat strikes the ball, the ball will gain velocity equal to twice the bat's velocity times the cosine of strike angle. The gain is independent of the ball's initial velocity. It's only the velocity of the bat and deflection angle that matter. The same physics applies to gravity assists. However, a faster spacecraft must fly closer to the planet to ...

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