# Tag Info

44

Rockets always seem to launch slower than I expect them for the thrust they can produce. Do they really launch off the pad at maximum thrust? In most cases, yes. For most orbital launchers, over 90% of the mass at liftoff consists of propellant. As the propellant is burned and exhausted, the mass rapidly decreases, and the rate of acceleration increases in ...

23

As in many things, shuttle was an exception, the answer for it is No. At liftoff the Space Shuttle Main Engines were running at a throttle setting of 100% of their rated power level. About 4 seconds after liftoff they throttled up to 104.5%. The maximum emergency throttle setting was 109%, but this was never used in flight. Screenshot from a Shuttle Mission ...

22

At least for some vehicles, "dynamic pressure is closely monitored" is not correct. You need to have an air data probe to actually monitor it, and not all vehicles do. Shuttle: Dynamic pressure was not actually measured1 during ascent so "Max Q" was not either. The magnitude and time of Max Q was predicted by prelaunch simulations, and ...

21

I'm always surprised when I see how slow they seem to budge from the pad. I know they're massive, but still. Remember that when you are in the vehicle, what you feel is acceleration, not speed, but when you are outside looking at it, what you see is mostly speed, not acceleration. Speed obviously starts at 0, and is the the result of the integration of ...

19

Certainly a reasonable question. A possibly useful mental model is to spin a bucket of water in some form. Initially only the surface layers will spin but each layer transfers motion to the next layer in and eventually the entity of the mass is spinning in a steady state. Similarly with the atmosphere over geologic time scales the atmosphere is spinning with ...

17

Shuttle: tl;dr - Shuttle throttled down based on the sensed acceleration. The "bobbling" about the 3g limit you see is because a proportional-integral control scheme was used and because the rate of change of the throttle command was limited. Details - The throttling algorithm works on an integral and proportional error. This algorithm tends to ...

14

The lower atmosphere must rotate with the earth because of friction---at least the very bottom of it. That is true, but only at the very, very bottom of the Earth's atmosphere, perhaps the last few millimeters. There are winds, after all. The trade winds and the prevailing westerlies (along with the discovery of how to beat against the wind) resulted in the ...

13

The engines of the Saturn V were not individually throttlable. Instead, in the first two stages, the center engine of the five-engine cluster was shut off entirely -- for the first stage, this is done for acceleration limiting at about 4g, and for the second stage it was done to reduce "pogo oscillation", a resonance between the engine and the rest ...

11

As Jörg W Mittag says, we don't know. But since they can gimbal all of the engines, I'd be surprised if they didn't. Gimbaling all of the engines a little, as opposed to gimbaling just a few of them a lot, has (at least) the following advantages: It generally maximizes the clearance between adjacent engine bells, since you're turning all the engines by the ...

9

We don't know. What we do know is that the Falcon 9 has engine-out capability which means you cannot pick a fixed setup beforehand, you have to be able to adapt to the loss of any one of the 9 engines. Other than that, everything is possible. We also know that SpaceX is constantly improving and changing, so what is true today is not necessarily true tomorrow ...

8

Simply stated, navigation equipment and software keep track of where the [vehicle] is located, guidance computes where it needs to be to satisfy mission requirements, and flight control gets it there. Sources: ASC GNC 2102 Ascent Guidance, Navigation, and Control Workbook (1979) G&C I/O/D 21002 Guidance and Control Insertion/Orbit/Deorbit Workbook (...

6

There are ways to measure dynamic pressure, and in aerodynamically complicated spacecraft (like the shuttle) if measured on its three four "nosecones" it could conceivably occur at (at least somewhat) different times in different places. And yet when we watch a launch there is a specific time when the announcer calls out "Max-Q!" at which ...

6

The center of mass of the Saturn V at liftoff is somewhat lower than you might expect -- 27 meters up, about a quarter of the way up the stack. This is because the upper stages are largely filled with liquid hydrogen, which is much less dense than the fuel and oxidizer in the first stage. Thus the yaw moves the upper end of the rocket much further than the ...

5

I have also been unable to implement PEG and struggled to find an adequate approach in my orbital launch sim. I have tried simply steering proportional to fraction-of-orbital-altitude-reached in the orbital insertion phase. I have tried various forms of quadratic guidance (inspired by the the Apollo LM's landing guidance). None have gotten good results. At ...

5

Supplementary answer only as this is a simulation based on data, not actual data. I went to flightclub.io and selected a simulation of the SpaceX Crew-1 mission. This is not real data it's an example of a simulation that likely fits various public data including videos of the launch. There are many more plots and tools there, and you can try adjusting ...

5

Nose away from tower, so tail moves slightly closer to, as seen in this video of the Antares ORB-2 launch.

5

To enjoy the greatest advantage from the Earth's rotation, you want two things: Launch from as close to the equator as possible. Launch as close to directly east as possible. The first part is fairly simple. The rotational velocity is proportional to $\cos(latitude)$, so the Guiana Space Centre gets over 99% of the effect, Kennedy Space Centre around 88%, ...

5

143 On the 24th of January 2021, the SpaceX Falcon 9 rideshare mission Transporter-1 deployed 143 satellites to a sun-synchronous orbit. (NASASpaceflight also made a labelled image) List of the satellites (roughly in order of deployment): 36 Planetlabs SuperDove cubesats 17 satellites at the Kepler port: 8 by Kepler Communications, 9 others A Maverick ...

5

Welcome to Space stack exchange. This is a part of launch window analysis and I'd recommend using that as a search term. The simplest answer is "a bit more than 180 degrees". This is for the situation where the launch site is on the equator and the target satellite is geostationary rather than inclined geosynchronous orbit. Imagine that the ...

4

In 1963 Project West Ford used a dispenser to place 480 million sub-satellites1 in orbit. 1Admittedly, very simple ones.

4

The atmosphere would rotate with the Earth surface but there are 2 major factors that affect it: Coriolis effect If you calculate what speeds each bit of the atmosphere would be moving at you'll find the largest speed at the equator and near 0 speed at the poles. In these situations fluid dynamics says the air will start rotating, creating vortices. This ...

4

Despite this, no one thought of making the launch vehicle / its payload orbit around earth, even for one revolution till the Russians did it on 4th Oct. 1957. Why so? This is not the case. Both the Soviet Union and the United States were extremely interested in the capabilities that Nazi Germany had developed during World War II. Both attempted to capture (...

4

The earth's rotation imparts to the rocket a free delta V of roughly 450 m/s if you launch straight eastward. About 464 m/s for eastward launch from the equator; it's less than that at higher latitudes (proportional to the cosine of the latitude), about 400 m/s from Canaveral, and less again if launching into higher inclinations. If you launch westward ...

4

The Soyuz_7K-OK_No.1 comes to mind. After an aborted launch, the launch escape system was triggered by the rotation of the earth. It fire approx. 27 minutes after the scrapped launch. Here's Scott Manley telling the story of this particular accident.

3

Getting to space is easy. Staying in space is hard. Staying in space is not about going up high. It is about going sideways really fast. From Navi Mumbai to Hyderabad is 600 km, space is only 100 km away. So, you are about 6× closer to space and about 200–300 km closer to the ISS than to Hyderabad, according to your profile. With a high-performance car, you ...

3

It's a matter of velocity. These rockets weren't capable of reaching Earth orbital velocity which is about 4.8 mi/s (7.7 km/s). Only at this velocity, when flying about parallel to the surface, the orbital perigee would no longer be within the Earth so that the craft would fall around the entire planet instead of falling onto the surface. V2 rockets for ...

3

It was in the onboard flight software, at least for shuttle. The second stage guidance software uses a cyclic, closed loop scheme to calculate the necessary commands to take the mated vehicle to a specified set of target MECO conditions. These conditions include cutoff velocity, radius from the Earth, flight path angle, orbital inclination, and longitude of ...

3

It is unlikely that gimbal checks would be done on a running engine (at least in flight) due to the resultant effects on the vehicle. Shuttle: In addition to the famous prelaunch gimbal test of the main engines prior to launch as described here, gimbal checks were also done on the Orbital Maneuvering Engines (OMEs) and the Solid Rocket Boosters (SRBs) thrust ...

2

It is a reasonable question, one that finds its answer in the concept of the planetary boundary layer. The rotating Earth, through its various irregularities on the surface and in topography, drags the atmosphere along. This vertical momentum transfer becomes weaker and weaker as one goes up in the vertical coordinate, until at a height of about ~1km the ...

2

If you search on YouTube "SpaceX NROL" then you get videos like this one The video only contains first stage recordings. When the engines start: T + 6:30 min 58.1 km 4,757 km/h When the engines stop: T + 6:58 min 31.1 km 2,245 km/h Then the speed increases until: T + 7:12 min 21.9 km 2,495 km / h Then the ...

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