Questions tagged [physics]
How physics applies to a particular activity in space or to getting to space.
289
questions
5
votes
2answers
711 views
What can be determined about an orbit if it passes through two points
Using a 3D Cartesian coordinate system if we know for certain that a craft will pass through two points in it's orbit (let's call them p1 and p2) and we also know the mass of the central body it is ...
1
vote
0answers
62 views
What is the best place on the internet to learn basic physics needed for rocket engineering? [closed]
Does anyone know a site where everything is in one place and it teaches equations and pricipals from the basics?
2
votes
1answer
167 views
Can a space craft realistically eject flares to evade a missile?
I was watching Behind Enemy Lines, and one of my favourite scenes is the jet attempting to evade the missiles.
All this got me thinking about the Defiant from Deep Space Nine, and some research shows ...
2
votes
0answers
34 views
Given 10W and a 100 square meter target to look for, which can search a larger area; SAR or LIDAR? (back of spherical cow-shaped envelope question)
Background
For the project discussed in Space based active optical sensors for maritime surveillance the concern seems to be that SAR is off the table because a low inclination orbit is in eclipse ...
2
votes
0answers
23 views
What is MAHLI's theoretical or expected best optical resolution? How was it defined? Was it verified on Mars?
The block quote in this answer to Has Curiosity ever taken a good hard look at the dirt covering its top surface? Can it? Have individual particles been sized? says that at a focus distance of 2.5 ...
23
votes
2answers
3k views
When burns are made during inefficient parts of the orbit, where does the lost energy go?
Any Kerbal Space Program player will know that burns prograde and retrograde to the velocity vector are most efficient closest to the body being orbited, while burns normal and anti-normal are most ...
3
votes
2answers
171 views
What is the theoretical smallest size limit for a phased array antenna that can reach LEO?
Now that one provider is operating a phased array ground-to-satellite internet comm system, others will follow. A frequently asked question is "When can we use Starlink with a sat phone?". ...
2
votes
0answers
164 views
What's the farthest an ISS astronaut gets from the station's center of mass during routine activities? At 0.5°/s what centrifugal effects are there?
This answer to Are there really “Dead End” signs on the outside of the International Space Station? won't be helpful here since for the purposes of this question spacewalks aren't part of routine ...
4
votes
2answers
326 views
Modeling a rocket using Tsiolkovsky's equation and ordinary differential equations
So I have this uni assignment to make a model out of ODEs, and my idea was to use rockets. After some research I found about Tsiolkovsky's equation and tried using it on a Falcon 9 (disconsidering ...
2
votes
1answer
133 views
Estimating thrust and kg fuel for a generation ship's journey to Alpha Centauri
Premise: A generation spaceship leaves Earth around the year 2060 on a journey to colonize Alpha Centauri A (ACA). In this fiction, fusion power is achieved in 2040, improved over 20 years, and used ...
36
votes
4answers
12k views
If an astronaut threw a cup of coffee into space, would it freeze, or boil off into gas?
If an astronaut threw a cup of coffee into space somehow, would it freeze into a block, or boil off into gas due to the zero pressure?
0
votes
2answers
130 views
Would hypothetical aliens from super-earths be larger and stronger then humans? [closed]
I’m curious how physics would affect the size and strength of human like aliens on super-earth worlds with 1 to 2 times the gravity of earth compared to humans. Would they be similar or be larger or ...
3
votes
0answers
79 views
How does Curiosity's X-ray diffractometer work? Does it measure only one angle at a time or does it have an area detector?
Per this answer to Are quasicrystals common on the Moon and Mars?, Curiosity has an X-ray diffractometer.
X-ray diffraction from 3D crystals can (begin to) be understood by embracing Bragg's law. A 3D ...
12
votes
1answer
3k views
Why can solid rockets be both the skinniest and most spherical launch vehicles while liquid fuel rockets have a more limited range of aspect ratios?
Question: Why can solid rockets be both the skinniest and most spherical launch vehicles while liquid fuel rockets have a more limited range of aspect ratios? Are there fundamental engineering ...
0
votes
0answers
61 views
Is a PhD in space-related technology from a Physics background possible?
I am 24 years old, from Argentina. Next year I will finish my 6-year degree in physics from the University of Buenos Aires (We've been told that it is equivalent to a master's degree, but maybe is ...
1
vote
1answer
155 views
If you travelled at exactly the speed of light, what would the stars look like behind you? [closed]
If you were in an Alcubierre drive bubble travelling at exactly 1 c, I wonder what it looks like if you looked back, to the direction you come from. If you went faster-than-light you'd obviously see ...
0
votes
1answer
91 views
Simple Ionic Drive Problem
I am having trouble with my calculated values for part B of the problem. In part A I used the formula F=qE, where F is the force, q is the charge = 1.6 * 10^-19 coulombs and E is the electric field = ...
11
votes
1answer
255 views
How much is 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
2answers
243 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
145 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
153 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
80 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
82 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
257 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
225 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
342 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
53 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
5k 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
291 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
120 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
135 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 ...
4
votes
1answer
561 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
100 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
53 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
vote
0answers
87 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
24 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
431 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 ...
3
votes
1answer
97 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
1k 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
383 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
85 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
113 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
50 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
123 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
3k 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
187 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
286 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
547 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
113 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 ...