43
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Why do rockets have multiple stages?
The basic reason: tossing an extra stage can be far, far, more of a mass-savings than trying to make one stage that can do everything.
There's a handful of reasons for this:
Engines weigh much less ...
- 10.6k
36
votes
Why did the space shuttle's altitude go down after reaching 108,000m?
The drop in acceleration around 40s into the flight is the shuttle throttling down to reduce the aerodynamic load on the vehicle. It then accelerates when past this point.
The drop in acceleration at ...
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25
votes
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Did any spacecraft ever use the Sun's gravity for acceleration?
It doesn't really work that way. We can use the Sun to change direction, but we need rocket thrust to increase speed with the msneuver.
To begin with, the closest stars (apart from the Sun) are not ...
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23
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Did any spacecraft ever use the Sun's gravity for acceleration?
The "gravitational" (slingshot) maneuvers space probes are performing are actually not so much about gravity. The gravity is method to "tie" temporarily these two bodies, but you could (purely ...
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23
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How to account for burned fuel mass when calculating spacecraft acceleration?
The quantity you ultimately need when planning your manoeuvre is change in velocity, which in spaceflight terminology is called delta-v, $\Delta v$ (searching this term would give you a lot of ...
22
votes
Why do rockets have multiple stages?
Then why not use only 1 stage?
Because we don't know how to do that.
That we don't know how to do make a single stage to orbit is a consequence Tsiolkovsky rocket equation and of the fact that some ...
- 73.2k
21
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How do vibrational isolators reduce the g-forces of a payload on a launch vehicle?
The g-forces from the rocket's acceleration remain unaffected, of course.
What the vibrational isolators do is isolate the payload from vibrations.
Without them, the payload would experience both the ...
20
votes
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SpaceX rocket strange velocity
Two possibilities: The Earth rotates at about 465 m/s at the equator. This video's measurements could include that speed, though I don't believe so as it starts from 0 m/s.
Most likely it's because ...
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19
votes
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How much acceleration g-force can prevent pilot from moving their arms?
According to the book Human Engineering guide for Equipment Designers, authored by Wesley E. Woodson and Donald W. Conover and published by the University of California Press, suggests the following ...
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14
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Why do rockets have multiple stages?
Other answers address the core construct of the rocket equation with words and equations, but here it is visually:
Where the Y-axis is the $\Delta V$ and the X-axis is the propellant mass. $b$ is a ...
- 9,685
13
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Did any spacecraft ever use the Sun's gravity for acceleration?
I think the question is based on a misconception about how gravity assists work.
If you just let yourself get pulled to a distant object then continue out the other side, the same gravity that ...
12
votes
Are we actually that close to techniques of accelerating probes to speeds like a quarter $c$?
Given that the interstellar medium (ISM) has a density of about 1 atom per cubic centimeter and given that laser propulsion could, in theory, accelerate a spacecraft to 30% of the speed of light in ...
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11
votes
Could you survive very high G's if your whole body was accelerated uniformly?
Of course.
(if you replace that pesky "infinite" with "arbitrarily large", physics really really hates infinite forces)
Who said you (and everything around you), is not currently ...
10
votes
Orbital Railgun for launching deep space probes
Let's look at some numbers. For the sake of argument let's target a delta-V from the railgun of 4 km/s enough to get to low lunar orbit or Mars transfer orbit.
If the railgun is 1km long, that would ...
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10
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Orbital Railgun for launching deep space probes
Concepts for mass-drivers or railguns situated on the moon exist.
What you're asking about is a mass driver space station in low earth orbit that a payload or ship launched from earth can dock with, ...
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9
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How do I calculate a rockets burn time from required velocity?
Alternate Wars gives this formula for computing the length of a rocket burn:
$$\Delta T = \frac {M_L E_V} {F} (1 - e ^ {-\frac {\Delta V } {E_V}}) $$
Where:
$\Delta T$: Length of burn in seconds
$...
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9
votes
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What is a non-propulsive vent?
It's simply a device that emits fluid in such a manner that there's no net force. Simple example, a T-shaped pipe where gas travels up the stem of the T and exits out both sides of the top bar.
A ...
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9
votes
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Theoretical Max G forces on Shuttle Launch?
Stealing the mass-at-MECO number from this answer, and using the 104.5% thrust numbers for 3 SSMEs from here, I get
(3 x (490,000) lbf / 308650 lbm ) = ~ 4.75 g's
Sanity check
(3 x (.65 x 490,000) ...
- 178k
9
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How do vibrational isolators reduce the g-forces of a payload on a launch vehicle?
The situation is a bit similar to driving up hill on a bumpy road.
The car's suspension definitely transfers the "average force" from the road up to the passengers, but let's talk about what ...
- 149k
9
votes
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Will DART fire its ion engine to accelerate prior to impact?
It almost does not matter, with a maximum acceleration of $0.6mm/s^2$ (1/16500th of a g),
the probe could only change its velocity by 1m/s over the last ten thousand kilometers of approach.
But no, ...
8
votes
How do vibrational isolators reduce the g-forces of a payload on a launch vehicle?
Other than the "DC" (or low frequency part) of the g-forces, all the "AC" (or high frequency components) of the g-forces create both positive and negative contribution to velocity ...
- 990
7
votes
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Soyuz seat - return
When the crew are going to return on a different Soyuz, they swap the seat liners beforehand.
"One of the first tasks for the Soyuz commanders after arrival was to swap the astronaut’s seat-liners to ...
- 10.1k
7
votes
What is a non-propulsive vent?
A non propulsive vent is an object designed to redirect venting gases into two opposing directions, such that the propulsive effects cancel each other out.
Here is a link to a photo of one use on ISS....
- 17.2k
7
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Did any spacecraft ever use the Sun's gravity for acceleration?
In constrast to the other answers here, I would like to point out that the Oberth Effect does allow you to gain kinetic energy from a gravity well without needing to rob it of momentum ... if you fire ...
- 359
7
votes
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Term disambiguation: acceleration with/without gravity
The terminology are (from Wikipedia)
Proper acceleration (force per unit mass(?); happens to have units of m/s^2)
co-ordinate acceleration (second derivative of position vector co-ordinates; has ...
- 990
7
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Term disambiguation: acceleration with/without gravity
But a free-falling accelerometer in a gravitational field will read a nice round zero.
That is the case for an ideal accelerometer. Real accelerometers have biases, scale factor errors, and all kinds ...
- 73.2k
7
votes
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Can something like SpinLaunch actually work?
Spin launch should work, but suffers from so many draw backs on Earth that it may well be impractical or limited to very niche or suborbital applications.
Huge accelerations will need to be applied ...
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6
votes
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Are we actually that close to techniques of accelerating probes to speeds like a quarter $c$?
The solar sail idea just works, tested and true.
Very powerful lasers are a reality. Very accurate, narrow-beam lasers are a reality too. Bringing these two together is absolutely doable.
Powering ...
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6
votes
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What precisely was the character of the non-gravitational acceleration of Oumuamua?
There is a paper on this subject that you can read here. Basically by fitting the data to a pure gravity simulation, there was some residuals, but when fitting it to the model $A_1r^2$, they could ...
- 121k
6
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Why did the space shuttle's altitude go down after reaching 108,000m?
For what it's worth, the Saturn V did the same thing getting to parking orbit. Different vehicles with different propulsion and staging, but the outcome is essentially the same:
Source: Saturn V ...
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