Questions tagged [physics]
How physics applies to a particular activity in space or to getting to space.
252
questions
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Masters in Space sciences after Aerospace Engineering [closed]
I'm currently in my first year of Aerospace Engineering and wish to pursue space sciences after graduation. Will I need some extra study in Physics other than my course to be able to successfully ...
4
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3answers
192 views
What happens if you jump on a “spin ship”?
If you're on a spin ship, or rotating wheel space station, and you jump, then you're no longer being accelerated by the rotation. What would happen?
First, I'll establish some terms to make discussing ...
2
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1answer
81 views
Are solar sail spirals logarithmic? Can this be shown analytically or by dimensional analysis alone?
There are several questions and answers here about spiraling towards or away from the Sun using solar sails tilted by roughly 45 degrees to convert the sunlight's incoming radial momentum into ...
6
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1answer
381 views
What is the terminal velocity of SpaceX Starship?
What is the terminal velocity of starship on earth and mars during descent?
Has SpaceX revealed or hinted the values of projected surface area and drag coefficient of the vehicle?
3
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1answer
159 views
Design of starship fins
How much can the falling speed of starship approximately be reduced by the bellyflop fall with fins? Are we talking about numbers around 5% or 50% here?
Wouldn't it make sense to put holes where the ...
31
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3answers
6k views
Does it make any scientific sense that a comet coming to crush Earth would appear “sideways” from a telescope and on the sky (from Earth)? [closed]
In multiple different movies and fiction, there's the threat of a burning space comet heading for Earth, threatening to kill everyone and destroy the planet.
One example is the animated Comet in ...
2
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1answer
80 views
Can I “tack” towards a laser beam from which I am powering my 100% efficient & massless ion engine?
As far as I know, for light and particles taking special relativity into account:
\begin{align}
E^2 &= (T + m_0c^2)^2\\
&= p^2 c^2 + m_0^2 c^4 &\text{ (particles)}\\[1.5em]
E &= p ...
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83 views
How should mass specific impulse calculated for relativistic exhaust?
This answer says:
Optimising for Isp only is problematic, as it's simply:
$$I_{sp} = \frac{v_e}{g}$$
Which is the same as optimising for exhaust velocity.
With no constraints on thrust, particle ...
2
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0answers
42 views
Why does Gravity Simulator's rendering of TESS' orbit look like a pretzel? How can I unpretzefy it?
Below is a screen shot from the amazing Gravity Simulator driven by our own @HappyKoala. If you haven't seen it recently go check it out now, then come back in 30 minutes and read the rest of my ...
0
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1answer
100 views
Could the crew of a spaceship with an Alcubierre warp drive survive if it only performs small “jumps”?
Could the crew of an Alcubierre drive-equipped spaceship avoid getting cooked alive by hawking radiation if their spaceship engaged and disengaged warp speed periodically over short distances?
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1answer
2k views
How hard is the hardest ice in the solar system? Is it in Pluto's ice mountains?
NPR's Pluto Has White-Capped Mountains, But Not Because There's Snow includes the following:
"Initially, it seemed logical that this high-altitude frost could form like on the Earth," says ...
4
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0answers
56 views
Did the Space Shuttle crew have to worry about the ionosphere? What relevant training or specific briefings did they receive?
Comments below this answer tell us that the Space Shuttle always remained in Earth's atmosphere. When it visited the Hubble Space Telescope or the ISS or Mir it was still in the thermosphere and ...
3
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2answers
185 views
How to determine heat transfer for survival on Venus?
I'm trying to determine how long a probe could survive on Venus' surface. Assuming its just a sphere of titanium with room temperature air inside, what would be the best method for determining the ...
4
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1answer
527 views
How efficient and fast would seven Caplan thrusters be at pushing the Sun and would it be worth building more than one?
I was thinking about stellar engines. One type of stellar engine is the Caplan thruster, which concentrates the star's light onto the star's surface to create beams of solar wind, which are collected ...
2
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0answers
105 views
Which deorbit trajectory minimizes reentry heating?
Atmospheric reentry, as I understand it, is a balancing act between minimizing delta-v needed and not burning up or breaking up in the atmosphere. The higher the velocity on reentry, the greater the ...
2
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1answer
46 views
Specific Heat Ratio for a perfect gas mixture
I am reading Rocket Propulsion Elements by George P. Sutton & Oscar Biblarz, 9th Edition. In the fifth chapter, I was introduce to the specific heat ratio k for the perfect gas mixture, Eq. 5-7:
(...
5
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1answer
326 views
Contracting rocket engine nozzles
The efficiency of rocket engine nozzles depends greatly on their expansion ratio an how well the ambient pressure matches the rocket nozzles exit pressure. An optimal expansion ratio means that there ...
3
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0answers
69 views
What is the maximum voltage of an Electric Sail?
Suppose we have an electric sail in LEO, how could one calculate the maximum voltage that could be sustained? It can't be infinite, there must be some limiting factors.
Is there any ionization voltage ...
2
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0answers
127 views
What exactly is electron precipitation in Earth's ionosphere and how does it relate to the STEVE phenomenon? [closed]
Source
Trying to decide if the unanswered question What was Steve? Is it called something else now? is in need of attention I checked Wikipedia's Steve (atmospheric phenomenon); Occurrence and cause ...
13
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2answers
2k views
Till what altitude above earth sounds can be heard?
In the new video of SpaceX SAOCOM 1B launch and landing RCS thrusters and other sounds can be heard during boostback burn. Falcon 9 boostback happens at nearly 100 Km altitude. Does the air density at ...
3
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1answer
213 views
What exactly gives a larger field of view to the donated “spy” telescopes that NASA may send to Mars? How much larger?
This answer links to Space.com's NASA May Launch Donated Spy Satellite Telescope to Mars which emphasized textsays:
An unexpected gift
The two donated telescopes were apparently built for a National ...
1
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0answers
75 views
I've looked at the Science involved but have doubts this would work, how can you generate momentum with-in a sealed system to produce propulsion? [closed]
Could you use a magnetic super-capacitor compound which is charged so it gains the maximum amount of weight\mass then is pushed away from the main object down a chamber using a magnetic field. As the ...
4
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2answers
143 views
Have there been any square 4U (2x2) cubesats?
How much did each MarCO 6U cubesat weigh? suggests that the density of a MarCO 6U cubesat might be as low as 0.75 g/cm^3 whereas I think they are usually about twice that.
That led me to speculate ...
2
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1answer
283 views
Did the Perseverance rover's Atlas 5 really “leap off the pad”? If so, was it because the payload is tiny, or because it's going to Mars?
Spaceflight Now's ULA’s Atlas 5 is NASA’s go-to rocket for nuclear-powered space probes quotes Tory Bruno, president and CEO of United Launch Alliance:
“This rocket is going to leap off the pad with ...
11
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1answer
1k views
Now that Perseverance is “hot” (RTG in place) and before it gets to deep space, how will it stay cool?
As soon as they are assembled MMRTGs continuously produce about 2,000 watts of heat energy. That dips only slightly when they are connected to a load and producing electrical power (about 125 watts ...
4
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1answer
165 views
Is there any possible reason to direct the electron gun specifically towards the ion trail behind an ion thruster?
This answer to Neutralization of ions in the ion thruster quotes the introduction to Wikipedia's Ion thruster:
Temporarily stored electrons are finally reinjected by a neutralizer in the cloud of ...
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0answers
105 views
Can Chemical Engineer work on something related to space?
I am an undergraduate student (scientific section) living in Qatar. I have a big interest in astronomy and astrophysics and have participated in the IOAA (International Olympiad on Astronomy and ...
0
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0answers
98 views
Roughly express how much of our Moon's apparent libration amplitude seen from the Geocenter is due to different effects?
My understanding is that when tidal locking of a body first happens it transitions from a state where the average rotation period is faster than the orbital period to a state where they are the same ...
4
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3answers
1k views
If a car or train freely drove on flat terrain on the Moon, would it eventually be stopped by something?
If you start an Apollo LRV on the Moon and let it go on flat terrain (with motor off), would it be stopped by ground friction eventually, or doesn't that stop a car? Same question for a train on rails ...
5
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1answer
864 views
Would a sniper bullet fired on Ceres reach orbital or even escape velocity?
What would happen if you fired a sniper bullet horizontally from the top of Ahuna Mons, the highest mountain of Ceres? Once I read somewhere that if you fired a bullet on the Moon in the correct angle,...
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0answers
135 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
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1answer
110 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
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1answer
87 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 ...
5
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1answer
117 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 ...
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0answers
116 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 ...
7
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1answer
193 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
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3answers
223 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
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1answer
135 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
61 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
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1answer
155 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
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1answer
139 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
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0answers
168 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 ...
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0answers
127 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
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1answer
431 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:...
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3answers
139 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
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1answer
141 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 ...
21
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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
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2answers
162 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
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3answers
735 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
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0answers
92 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 ...
