68

Well, gee, this question may as well have my name printed directly on it! Spacecraft protection from the orbital debris threat comes in two flavors: Shield and withstand Detect and avoid To start, page 5 of this NASA paper presents a good first-order approximation of the general LEO orbital debris threat. You'll see some variation with altitude and ...


49

Possibly Mecca, Google image search indirectly led me to a facebook post dated 4th September claiming to be Sergey Ryazanskiy's claiming the images were of Mecca. If this is the case the uplight may be the Makkah Royal Clock Tower, which according to wikipedia "On special occasions such as new year, 16 bands of vertical lights shoot 10 km (6.2 mi) up into ...


48

Well I confirmed via Google Maps that this is Mecca. As shown in the map and image below the roads align with those lighted in the image. The dark areas in the first image are steep hills to the East. The brightly lit region is the Kaaba and large Masjid al-Haram Mosque, and the bright up light is indeed the Makkah Royal Clock Tower.


37

This appears to be an error that has propagated from paper to paper over the years. Examining the original paper cited by all these other authors, "Effects of the March 1989 Solar Activity" by Allen et al. shows us that the actual altitude loss was 3 miles (not 30 km) and the satellite in question was "the aging NASA satellite SMM" aka Solar Maximum Mission, ...


36

The answer to your title question "Why not travel to Mars in 2 months?" has already been answered. Money. Lots and lots of money. We should first note that the answer to a different question: "Why haven't people gone to Mars?" is much the same. Money. However the amount of money to go there in two months is many times greater than the money to go there ...


35

The easiest to see ISS orbital reboosts is by checking Height of the ISS (where with height they mean orbital altitude above mean sea-level) over at Heavens Above. For example, for the last year, this is the graph: This plot shows the orbital height of the ISS over the last year. Clearly visible are the re-boosts which suddenly increase the height,...


34

The answer varies with atmospheric density (due to varying solar activity), with satellite geometry and mass, and with attitude. But for a typical 3U cubesat, the minimum altitude for a circular orbit to complete at least one revolution is approximately 150 km. My colleagues and I collected the following orbital data from a cubesat we were operating: The ...


32

As Undo mentioned, the type of orbit is called a retrograde. A pure retrograde orbit is quite rare, in fact, NORAD currently isn't tracking any (unclassified) objects with a 180 inclination (Pure Retrograde). However, there are a fair number of satellites with a retrograde inclination (Over 90 degrees). Of particular note is the Sun Synchronous orbits of ...


31

ISS orbits most of its time in what is called a Torque Equilibrium Attitude (TEA). Since gravitational acceleration varies depending on distance from the Earth, non-symmetric objects of any appreciable size have a net torque acting on them that is attitude-dependent, relative to the local vertical/local horizontal. For the most part, the ISS's attitude is ...


31

No, a quick calculation yields a $\Delta v$ of about 4.6 km/s and you need about 9 km/s to get to low-Earth orbit. You'll lose a lot of that velocity to aerodynamic drag as well as the vertical portion of the flight, so a rough estimate of the final speed at burnout would be somewhere around 3 km/s -- or about 10,000 km/h. Using the specifications from the ...


31

There's a few pieces of information that are needed to explain why one might be wary of 1 cm objects: Objects as small as 4 inches (about 10 cm) can be seen by radars or optical telescopes on Earth Oops, can't see 'em. There are also millions of pieces of debris smaller than a third of an inch (1 cm). In Low Earth-orbit, objects travel at 4 miles (7 ...


30

There are limits. For one, there's atmospheric effects that scatter light in visible wavelength spectrum. You might be able to penetrate clouds and haze easier in the lower end of the spectrum and towards the infrared wavelengths, and those might still be usable for facial recognition though. Another limit is aperture of optical equipment used to take ...


30

By convention the altitude of a spacecraft is the distance to the center of the Earth minus roughly 6378 kilometers, or some reference radius that is representative of the equatorial radius of the Earth. Spacecraft altitude is not really used as a precise description of a satellite's position, since its only a scalar and it requires a definition, but if you ...


27

would the photography be good enough for facial recognition? Not yet. It's not even close. Facial recognition requires 50 to 100 pixels between the eyes, or on the order of 1 millimeter resolution. To see that kind of detail from a distance of 250 kilometers using blue-green light (500 nm) would require a lens or mirror that is 125 meters in diameter. Note: ...


27

After reading @OrganicMarble's answer and the link there as well, I looked at the TLEs for the Solar Maximum Mission in 1989 (1980-014A, 11703) and while the altitude loss in March does not seem to be in any way dramatic overall, there is in fact a drop in the average altitude at the time. I've propagated the TLEs for one complete orbit starting at the ...


25

JWST is being launched on an Ariane V with a cryogenic upper stage. That upper stage has to be used immediately to launch it on a trajectory to the Sun-Earth L2. The stage operates on batteries, and the cryogenic fuel is boiling off. So there would be no time to do anything even if you deployed the telescope before departure. Furthermore, the deployed ...


25

Nodal precession doesn't matter for a plane of satellites like this, they will rotate around in unison, so the coverage will remain the same. Okay, so why the unusual dual inclination constellation? The inclination of a satellite band tends to let you know what latitude it will work best at. A 0 degree satellite works best at the equator, a 90 at the poles. ...


23

The altitude difference is minor compared to the plane change. Even 23 degrees of plane change would require a prohibitively large change in velocity 2 * 7.5 km/s * sin(23 degrees / 2) = 3.0 km/s In reality the plane change required is greater than 23 degrees, because the two orbits don't have the same right ascension of ascending node. Hubble actually ...


23

First of all, LEO isn't just reaching 160 km, it's reaching there and moving at a very fast speed. In fact, 160 km would be a really poor orbit, you really need something more like 350 km to get anything practical done. As to your question, yes, it is theoretically possible. In fact, there have been a few amateur made rockets that have reached the Kármán ...


23

Spacecraft rely on information from earth to avoid space debris, they don't have instruments for scanning and detecting debris. There's a few reasons for this: Power: most spacecraft don't have enough electrical power to run a radar powerful enough to detect small debris far enough away to matter Weight: in order to be useful for detecting debris the radar ...


23

FORMOSAT-5 was deployed directly to a 720 km circular orbit, with only a single burn. In order to do a circular orbit so high, one has to have a more vertical ascent then would be typical. Basically, one has to be burning a significant amount of time near the apogee, which has to be 720 km in this instance. For a lower perigee insertion orbit, say 200-300 km,...


23

Skylab's science experiments included Earth surface observations, and the higher inclination orbit allowed more surface to be viewed. Per Living and Working In Space: The NASA History of Skylab: The requirements of the earth-resource experiments caused major changes to mission plans. Primary among these was an increase in orbital inclination to 50º. ...


22

According to Wikipedia on Low Earth orbit: A low Earth orbit (LEO) is generally defined as an orbit below an altitude of approximately 2,000 kilometers (1,200 mi). Given the rapid orbital decay of objects below approximately 200 kilometers (120 mi), the commonly accepted definition for LEO is between 160 kilometers (99 mi) (with a period of about ...


22

Using the links in Erik's answer and comments, I threw this together. #!/usr/bin/python3 """ (C) 2014 Dotan Cohen This program is free software: you can redistribute it and/or modify it under the terms of the GNU General Public License version 3. http://www.gnu.org/licenses/gpl-3.0.html """ import re import time import urllib.request from bs4 import ...


21

Spacesuit designers and extravehicular activity (EVA) planners would probably prefer if spacewalks only took part in the Earth's shadow. From the spacesuit design perspective, one of the biggest issues is heat rejection, not heat retention. This is because of nearly nonexistent convective heat transfer (conduction and advection) in near vacuum in LEO so the ...


21

In this pic the angle $\phi$ is asin(6378/6878) or about 68º. It stays in the shade over 2 * 68º or about 136º. That's about 38% of the period. That's 2145 seconds or about 36 minutes. This is what the orbit would be during the fall or spring equinox. Other times of the year it could be shorter. In this pic I assume the sun's ray's are parallel. A more ...


20

The South Atlantic Anomaly is a region of high particle flux above the Atlantic Ocean off the coast of Brazil, caused by a slightly lower magnetic field above this point on the Earth. The problem it causes satellites is that above the anomaly, the magnetic field being weaker allows particles to get closer to the Earth. These particles can damage detectors ...


20

The short answer: 2-4 times per year the ISS enters a "full sun" period. Right before this happens, the ISS will line up near the terminator at the beginning and the end of this period. Full answer: I'll try and cover this without explaining too much orbital mechanics. The key thing is what is known as the beta angle, which is the angle between the sun and ...


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