Questions tagged [physics]
How physics applies to a particular activity in space or to getting to space.
223
questions
4
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1answer
99 views
Can an electrostatic shield provide protection from the Van Allen belt?
Would an electrostatic shield provide enough protection for a crewed space craft to survive in the Van Allen belt for more then an hour?
5
votes
1answer
95 views
Would there be snow, rain, fog or clouds in a deep, sealed, subsurface cavern on the Moon if water were present?
The question Most efficient method of storing energy with water on the moon? proposes a several hundred meeter tall subsurface cavern on the Moon. I added the following comment to an answer:
I keep ...
1
vote
1answer
80 views
Interactions between rocket exhaust and radio communications?
Rocket exhaust is bright in visible light, we can still see through it but when there's hot, glowing soot it's so bright that we think it's opaque, but it's not. See answers to How does the camera ...
2
votes
1answer
63 views
Where can I learn to calculate the physics of an ion thruster?
I am trying to build an ion thruster, but I don’t know where to start learning the actual numbers behind one. I know how they work on a basic level, but not much more.
Basically I want to be able to ...
1
vote
0answers
107 views
Kepler prediction problem, fundamentals of astrodynamics
I needed help with problem 4.3 of Fundamentals of Astrodynamics by Roger R. Bate, Donald D. Mueller, Jerry E. White (dover, archive.org)
Given that $r_0 = (I+j)$ and $v_0 = 2k$ find $r$ and $v$ for ...
6
votes
1answer
168 views
With a 10% increase in Earth's mass, would the Karman line move up or down, and by how much?
This is an exercise to better understand the basic physics and math behind scale height and the Karman line. It was inspired by this answer to Why is FAI considering lowering the Karman Line to 80km? (...
3
votes
3answers
188 views
What (if anything) limits the efficiency of a rocket engine?
Humans have developed lots of rockets. I observe that in most cases to increase the payload capacity we just increase the amount of fuel.
Is it not possible to exponentially increase the efficiency ...
1
vote
0answers
33 views
Would the Yarkovsky effect ever be faster than a solar sail from a 1 AU orbit to the Sun?
Previously I'd mistakenly asked Would the Poynting–Robertson effect ever be faster than a solar sail from a 1 AU orbit to the Sun? when I'd meant to ask about the Yarkovsky effect which can be much ...
0
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1answer
55 views
Could a skyhook be used to change a satelites orbit from polar to equitorial?
Could this work if the skyhook also had ion engines to maintain its orbit or would the cable just snap?
-1
votes
1answer
148 views
Can I do “car surfing” on empty space? [closed]
Suppose a Car/Van is launched into space with you. Suppose you would like to do 'Surf' on the car roof like Marty in "Teen Wolf". On the earth, if car accelerate up to 30-50 or 100 mph will make Marty ...
3
votes
0answers
49 views
Why might krypton have a lower utilization fraction than xenon for ion propulsion, and what can be done to improve it?
A comment below Why will Starlink satellites use krypton instead of xenon for electric propulsion? links to the 2011 preprint A Performance Comparison of Xenon and KryptonPropellant on an SPT-100 Hall ...
5
votes
0answers
165 views
What exactly is a solar gravity well manouver and in what cases would it be helpful?
In this answer to the gedankenexperiment question With current state of technology if we wanted how long would it take for newly launched probe to overtake Voyagers? I've seen the term "solar gravity ...
1
vote
0answers
55 views
Is centripetal acceleration around an ellipse with constant tangential velocity always pointed towards the center of the ellipse? [closed]
I've tried to find answers online but surprisingly couldn't find any.
8
votes
1answer
424 views
What do the shaded vertical lines in the animation of Gravity assists of space probes, mean?
Example Animations from Wikipedia —
https://en.wikipedia.org/wiki/Gravity_assist#/media/File:Animation_of_Voyager_1_trajectory.gif
https://en.wikipedia.org/wiki/File:...
-1
votes
3answers
128 views
Would the trajectory of a comet be altered by attaching a parachute to it?
I am curious to know if the trajectory of a comet that is on a collision course for Earth could be altered by simply attaching a parachute to it. The parachute interacting with the comet's tail should ...
0
votes
1answer
111 views
Would the Poynting–Robertson effect ever be faster than a solar sail from a 1 AU orbit to the Sun?
In this answer to Do you need 0 km/s velocity to crash into the sun? I mention solar sails for retrograde thrust and the Poynting–Robertson as two ways an object could ever-so-slowly spiral into the ...
19
votes
7answers
8k views
Do you need 0 km/s velocity to crash into the sun?
I was reading a popular thread about the delta-v required to escape the solar system compared to the delta-v required to crash into the sun. I get it: the earth itself already has a high speed (29.7km/...
2
votes
2answers
133 views
Are there some three-body orbits that can't be escaped? Can we know without propagating forever?
update: Searching for "choreographies" I found this Physics SE question which is related but different because it asks only if periodic solutions can be proven to be periodic numerically and my ...
7
votes
3answers
599 views
Why does this formula say rocket efficiency depends on velocity?
Wikipedia gives the following equation for the efficiency $\eta_p$ of an engine here:
$$\eta_p= \frac {2\, (\frac {v} {v_e})} {1 + ( \frac {v} {v_e} )^2 }$$
where $v$ is the rocket speed and $v_e$ ...
2
votes
0answers
79 views
What was Steve? Is it called something else now?
"Steve" was a temporary name for a space phenomenon above the Earth. Since then it's likely much work as been done and a more permanent name chosen. So I'd like to ask what Steve really was/is, and if ...
4
votes
1answer
90 views
How to find the moment of inertia of the Viking capsule?
I have an assignment where I have to simulate a Mars re-entry using the Viking capsule. I have finished it but now I want to go further and try to make my capsule glide. For this I need to enslave the ...
9
votes
5answers
1k views
Why do space rockets not start from an angle? Why go straight up? [duplicate]
I know that they used to have this idea, back in the day, of a "space gun" to fire somebody into space, and I understand why that was not safe or practical/feasible.
However, once they had come up ...
1
vote
1answer
50 views
Can anyone recommend a good online calculator for travel time within the solar system?
I'm trying to figure out how long it would take to travel to saturn with a skyhook launch from moon orbit.
1
vote
1answer
42 views
What exactly is eLISA, how will it benefit from LISA Pathfinder and how large will it be?
This answer to What do the gravitational wave findings mean for Evolved Laser Interferometer Space Antenna satellite says:
Given that the LPF is already launched, I doubt that it will be cancelled. ...
0
votes
1answer
110 views
For a DAWN-like solar-electric deep space mission, would using propellant particles much heavier than xenon atoms be beneficial?
For deep space missions using ion propulsion that are power-limited, this answer explains that a large mass/charge ratio ($m/q$) species is desirable. The solar-electric propulsion system used by the ...
6
votes
2answers
172 views
How can a meteor gain energy in an encounter with the Earth even though these answers say it can't?
The question Did a spacecraft ever use an atmosphere to accelerate away from a planet? was unfortunately given five down votes and answered with:
Entering the atmosphere introduces drag, which could ...
2
votes
0answers
43 views
Cartesian vectors to keplerian orbital elements of binary system
I am looking to code a a function that converts my 3d position and 3d velocity of a binary system into keplerian orbital elements of the system. I have seen a few other posts on this but they always ...
0
votes
1answer
73 views
If a spaceship were to lose all fuel, where does it go? [duplicate]
If a spaceship were to run out of fuel mid-flight, and it was between two solar systems, one with 2 suns and 6 planets, and one with 1 star and 10 planets, where does it go? I feel like I’m missing ...
1
vote
1answer
205 views
How did NASA calculate 22 million “rocket horsepower” for the SLS Booster?
This answer to Does NASA really report the power of rockets in horsepower? cites NASA news item Space Launch System Booster Aimed and Ready to Fire which says
"What's impressive about this test is ...
5
votes
1answer
263 views
Is there some fundamental limitation that would prevent steam-powered rockets from reaching space?
According to the Discovery Channel (see CNN article below) the latest attempt to use compressed steam propulsion to get to 5000 feet ended in tragedy. It's not yet clear the altitude it reached, ...
2
votes
1answer
90 views
Would a small electron microscope in a cubesat work well in space at 400 km?
There is now an electron microscope in space!
Suppose that once I win a lottery I can build a small, modest SEM column and put it in a 6U cubesat that opens one side to allow the electron optics to ...
4
votes
1answer
278 views
In layman's terms, how hot will the skin of a spacecraft become, 144 million miles from the Sun?
Ok, last week I asked how hot would a piece of metal become at a distance from Earth to Mars facing the Sun. Thank you for all the nice replies, but I do not have much math knowledge. So let me ...
-3
votes
1answer
201 views
temperatures of metal facing the sun in space
If a piece of metal were orbiting the Sun at the distance from earth to Mars, always facing the sun, what would it's temperature be.
0
votes
3answers
328 views
How to solve this exercise in orbital mechanics; the moon stops in its orbit, what happens next?
As an exercise in orbital mechanics, suppose the moon were to suddenly stop orbiting Earth, and instead at time $t=0$ begin moving in the same direction as Earth so that their relative velocity were ...
1
vote
1answer
176 views
How to calculate slowing effect of a planets gravity on a projectile that is launched upwards
The acceleration a ballistic projectile would experience at a certain height above a planet (neglecting any atmosphere) is given by
$$a = -\frac{GM}{(R + h)^2}$$
where
$G$ is the gravitational ...
2
votes
0answers
66 views
How much energy would be needed to liquify 1 gram of atmospheric oxygen on Mars?
I've been told I have no Moxie but I still need oxygen to live on Mars. I see that Mars' atmosphere is 0.14% oxygen and my sad moxiless self wants some.
I want to make a low power refrigerator to ...
3
votes
2answers
216 views
What does Earth's J₂₂ moment look like?
Wikipedia's Geopotential model give's the form of the potential component linked to $J_2$ as
$$u = J_2\frac{P^0_2(\sin \theta)}{r^3} = J_2\frac{1}{r^3}\frac{1}{2} \left(3 \sin^2\theta-1 \right) = ...
1
vote
1answer
149 views
What is a lithium fed GIT? How does it work?
This answer to What is the maximum speed an ion engine can propel a spacecraft at? mentions the following:
Lithium fed GIT (gridded ion thrusters) have demonstrated 50,000 - 80,000 seconds of ISP (...
1
vote
0answers
101 views
Would it be possible to make a bubbleworld in an asteroid? [duplicate]
Would it be possible to drill a bore hole into an asteroid, fill it with water tanks and use sunlight to blow a hole large enough to fit a rotating space station inside, seal it off and fill it with ...
4
votes
1answer
110 views
Analytical treatment of relative positions between satellites?
I have been searching the internet for estimation of relative position between two satellites. However, all sources seem to be pointing to methods used for proximity operations, where the math ...
4
votes
1answer
126 views
What does S represent in Chris Hadfield's D = ½ ρ v² S?
Retired test pilot, CSA astronaut and ISS Commander Chris Hadfield's new Master Class advertisement video Chris Hadfield Teaches Space Exploration - Official Trailer - MasterClass is heavily edited ...
12
votes
1answer
710 views
Does the “Tennis Racket Theorem” apply to the ISS? Does it rotate around its intermediate (unstable) axis?
Wikipedia's Tennis racket theorem begins:
The tennis racket theorem or intermediate axis theorem is a result in classical mechanics describing the movement of a rigid body with three distinct ...
59
votes
6answers
10k views
When was Newton “not good enough” for spaceflight; first use and first absolute requirement for relativistic corrections?
Concepts in Special Relativity (1905) and of General relativity (first developed between 1907 and 1915) substantially predated spaceflight; they were well known and had been tested well before objects ...
2
votes
1answer
134 views
Space and Newton laws
I've read some articles which explain that we can't totally rely on Newtonian gravity concepts for understanding the motion of objects in space.
My question is how the use of relativity helps us to ...
1
vote
2answers
87 views
Given r/a, what are the limits on the direction that an orbiting body could be moving (e.g. solid angle vs r/a)?
An orbiting object at distance $r$ and semimajor axis $a$ will move at $\sqrt{2 - \displaystyle \frac{r}{a}}$ times the speed of a circular orbit at $r$, no matter what the eccentricity or which ...
1
vote
1answer
99 views
When is it okay or at least helpful to use energy arguments in orbital mechanics?
When faced with energy-based questions about spaceflight we often comment something like orbits are about momentum, not energy and use delta-v math in answers.
But in this answer to How big a nuke ...
0
votes
2answers
186 views
How big a nuke would be needed to break Phobos out of orbit?
Phobos
Radius: 11.267 km
Orbital period: 8 hours
Equatorial rotation velocity: 11.0 km/h (6.8 mph) (at longest axis)
With an 8 hour orbit around Mars it must be going at a fair clip already which ...
5
votes
1answer
208 views
Explain this light and wavelength graph
Would someone please explain this graph. I am not an expert and with my limited understanding of physics, I am unable to correlate this graph between the light received with its wavelength.
I don't ...
4
votes
1answer
310 views
Why don't spacecraft get left behind once in deep space?
On earth, I know that if I throw a tennis ball straight up while in a car, it comes straight back down thanks to Newton's first law. The ball, the air in the car, and myself are all moving at a speed, ...
48
votes
6answers
14k views
Is it possible for a moon to have a higher surface gravity than the planet it is attached to?
Is it possible that a moon has a higher surface gravity than its planet? I guess it would mean that the moon has a higher mass, but then it would be the planet gravitating around the moon and the ...
