Questions tagged [physics]
How physics applies to a particular activity in space or to getting to space.
271
questions
2
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0answers
20 views
How much is really known about those liquid metal droplets orbiting the Earth? (e.g. sizes, composition, orbits…) Are any actually tracked?
The question Orbit Guardians - bs, right? mentions a company proposing a smallsat that will capture then give a roughly 200 m/s retrograde "kick" to liquid metal NaK alloy droplets in LEO ...
2
votes
3answers
152 views
Why is hydrogen better than helium as remass?
I just watched a very good YouTube video on why nuclear engines might be useful, and it also goes into why Hall Effect thrusters are super good at squeezing obscene ISP out of things.
During the video,...
2
votes
1answer
99 views
How do grid fins actually work? Which aerodynamic mechanism(s) produce the torque on the spacecraft?
I’m trying to model the steering force that grid fins exert on a falcon 9.
I know these things are not just grid-shaped fins but actually grids of fins.
And each of those fins will experience drag and ...
2
votes
1answer
135 views
How difficult to gravity assist brake on entry to Alpha Centauri system? [duplicate]
Say a generation ship arriving at Alpha Centauri A system wants to get into orbit (or land) on an exoplanet there. After decelerating for the 2nd half of the journey, their approach velocity is still ...
4
votes
1answer
62 views
Kinetic reaction from emission of electromagnetic radiation
If an object is emitting 1 watt of electromagnetic radiation directionally and has negligible black body radiation, how much thrust is produced? How can you calculate this generally?
1
vote
1answer
73 views
Since Vesta is rotating, could you dig a habitat into it near the poles?
Would building a crescent shaped habitat work if you didn't want to go all the way?
Edit: I'm asking if this would be enough to provide artificial gravity, sorry not not being clear about it.
2
votes
1answer
205 views
When does a specific equipment at a certain temperature start to freeze in interstellar space?
This is my first post here. I'm working on a project which involves a number of problems and some parts of that are related to empty space and space exploration. I try to be focused and reflect one of ...
3
votes
1answer
165 views
Pendulum rocket fallacy - so why *do* skyrockets have sticks?
This question is inspired by two, linked questions.
Skyrockets (of the pyrotechnic/firework kind) have guide sticks, which are (according to internet sources) to enhance stability: "The guide ...
9
votes
1answer
259 views
Star-shaped artifacts in SAR images of the “Suez Canal traffic jam seen from space”
Wikipedia's 2021 Suez Canal obstruction links to the Sentinel-1 synthetic aperture radar (SAR) image of the
Traffic jam in the Gulf of Suez caused by the obstruction as seen by the Sentinel-1 ...
0
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0answers
51 views
Help understanding vectors in diagram from “Magnetohydrodynamic flow control during reentry” and the actual goal of this research
A link to the ESA Advanced Concepts Team page Magnetohydrodynamic flow control during reentry was recently shared under Re-entry Heat Shield Alternative. It says:
During the reentry phase, spacecraft ...
18
votes
4answers
4k views
What is the “pendulum rocket fallacy” as it relates to analogizing a pencil balanced on a finger to maintaining attitude of a hovering rocket?
I've received comments that explain to me that the analogy between rocket attitude control during a hovering maneuver and the act of balancing pencil on the end of a finger is a helpful and good one; ...
4
votes
0answers
190 views
How do you “make” a soliton? (recent peer-reviewed theoretical work in FTL travel)
I've just read an Article on the new approach on Warp Drives Dr. Erik Lentz describes. Instead of creating a bubble with negative energy density, he describes a Soliton in spacetime, which he ...
2
votes
2answers
68 views
Oberth Effect in Solar Sails: Where does the extra energy comes from?
Suppose, the reflectors of Solar Sails are opened for same amount of time at both periapsis and apoapsis. How does Oberth effect work in this case? Will Delta-V be same and hence change in Kinetic ...
1
vote
1answer
126 views
When they shoot lasers at the Moon for ranging, what is the shape of the beam?
Laser ranging of the Moon is usually done with a Q-switched pulsed laser fed into a big (1 or 2 meter diameter) telescope as a collimator in order to get a tight beam all the way to the Moon in hopes ...
3
votes
1answer
396 views
Understanding the rocket equation - calculating Starship delta v
I am trying to calculate delta v of Starship - both as separate stages (Starship [SS], Super Heavy [SH]) and as a fully stacked rocket including 100t payload.
I know that I have to calculate 2 ...
-1
votes
1answer
97 views
what would happen if there were windmills in space? [closed]
If there was a windmill in space and you spun it, would it spin forever creating infinite energy? or would it somehow slow down or not create energy? if instead of wind you used magnets to spin the ...
1
vote
0answers
51 views
Sources for values for realistic thrust calculation exercise?
I want to use this simplified equation to calculate the thrust of multiple different real engines:
$$F = \dot{m} V_e + (p_e - p_0) A_e$$
Source: https://www.grc.nasa.gov/www/k-12/airplane/rockth....
1
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0answers
43 views
How to find/extract the semi-major axis from a TLE with Skyfield?
I have a TLE:
1 33591U 09005A 21024.46740879 .00000049 00000-0 52095-4 0 9997
2 33591 99.1927 41.5349 0014084 172.6670 187.4709 14.12449679616592
And I would like ...
1
vote
0answers
22 views
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
votes
3answers
265 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
votes
1answer
87 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
votes
1answer
804 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
votes
2answers
290 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
votes
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
votes
1answer
83 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 ...
0
votes
0answers
96 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
votes
0answers
44 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
votes
1answer
108 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?
10
votes
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
votes
1answer
168 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
votes
2answers
226 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
votes
1answer
536 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
votes
0answers
111 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
votes
1answer
51 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
votes
1answer
368 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
votes
0answers
71 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
votes
0answers
131 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 ...
14
votes
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
votes
1answer
221 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
vote
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
votes
2answers
158 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
votes
1answer
307 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 ...
13
votes
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
votes
1answer
168 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 ...
1
vote
0answers
167 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
votes
0answers
99 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
votes
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
votes
1answer
950 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,...
4
votes
0answers
138 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
111 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 ...
