Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now
19

Biprop attitude control thrusters using UDMH and N2O4 in a docked Progress vehicle are used to reboost ISS using about four Progress vehicles a year. More recently, ESA's ATVs have also been doing reboosts using MMH/N2O4 thrusters. On the order of 2 m/s per month is required.


17

You are most likely seeing an artifact of how JPL represents its ephemerides for fast numerical computation. JPL integrates the equations of motion over time. This inevitably results in mismatches between the integrated state and observations. These errors are used to adjust initial states and the integration is then re-performed. The cycle stops when the ...


16

According to Wikipedia, the delta-v requirements to stay at L1 or L2 are about 30-100 m/s per year. That seems quite high, however, more likely is around 5-16 m/s. The sun shield has an area of about 300 m^2. The thrust possible is about 0.00279664 N, assuming purely reflective. Mass of JWST is about 6200 kg. Putting all of that together, the possible ...


13

First, there are several forces acting on a sailcraft. Aerodynamic drag Solar radiation pressure Gravity field non-sphericity Electrodynamic drag If you go anywhere lower than 770 km, atmospheric drag is by far the largest force that pulls your apoapsis down. Quoting Vulpetti (2008): When unfurled in LEO, the drag on the sail produced by its flight ...


13

As noted by @asdfex, 440N and 22N are convenient round numbers in imperial units: 100 lb-f and 5 lb-f. The exact thrust values for small spacecraft maneuvering thrusters aren't usually critical to designs of those craft; if the thruster is a little larger or smaller, maneuvers will just take a little less or a little more time. Thus standardized, known-...


12

In addition to Progress and ATV vehicles, docked at the aft end of Zvezda, using their main engines to boost the orbit, the Zvezda module also has engines that can be used. In fact, the Progress cargo vehicles can refuel the Zvezda module. From Wikipedia: The two main engines on Zvezda can be used to raise the station's altitude. This was done on April ...


12

According to the James Webb Space Telescope Initial Mid-Course Correction Monte Carlo Implementation using Task Parallelism, J. Petersen et al. (PDF): 3.1 Propulsion System Overview Two sets of thrusters comprise the observatory’s propulsion system. The first is a set of Secondary Combustion Augmented Thrusters (SCATs) that are the main thrusters ...


11

The ball of water in that picture is in orbit; it's just surrounded by (presumably) the ISS. But a ball of water like that definitely cannot survive in the vacuum of space. Below a certain pressure, water can only be water vapor or ice. So a ball like that would immediately start to boil if it were surrounded by a vacuum. The water vapor would quickly ...


8

Most geostationary satellites are kept within a very small margin, about 0.5 degrees. Wobbling happens due to a number of factors, including the Sun, Moon, and flattening of Earth at it's poles, causes some precession to occur (Wikipedia). It requires about 50 m/s of delta v to remain in a geostationary orbit per year, due to this effect. In addition, solar ...


8

The main difference between the two is that halo orbits tend to be much larger and are constricted to one plane. There's a NASA tech doc from 1993 comparing the station keeping costs between the two and finding none. The authors were quite clear that they did not know if this applied to all station keeping algorithms, but it was clear in the one they ...


8

Yes, GPS satellites do execute station keeping maneuvers. Primary purpose is to keep them within the desired repeating ground track, which leads to a maneuver every year or so for each satellite. I believe primary source of disturbances at that altitude are geodetic variations in gravity field. The maneuvers are needed less than once a year on average. Of ...


8

This paper by Heiligers et al. explores Earth-moon libration point orbits with the addition of solar sail thrusting. While it is of course not directly translateable to Sun-Earth L2 (JWST) the dynamics of libration point orbits in both systems are at least comparable. The study shows that an increase in stability can be acquired for some orbits (lunar L2 ...


8

tl;dr: Park your ISS-like space station above 700 km and there is a good chance it will only lose 100 m/s in 1,000 years due to atmospheric drag at least (and 2000 km for a million years). However, there are other problems This is a really interesting question! Just for example, the LAGEOS satellites are about 6,000 km above the Earth's surface and are ...


7

the VASIMR test planned by Ad Astra has been cancelled: On December 8, 2008, Ad Astra signed an agreement with NASA to arrange the placement and testing of a flight version of the VASIMR, the VF-200, on the International Space Station (ISS),[24] but the plan was scrapped in 2015. The reason: But a series of agreements with NASA, dating back to ...


7

Between atmospheric drag out through almost 1000km, there's the issue that solar light and solar wind are both cut by the passing into the shadow of a planet. Since this puts more of the energy on the solar side, even for high orbits, the sail is, if passively deployed, making the orbit more ellipsoid and thrusting it planetward on the sunward lobe. Let's ...


6

Your question is hard to answer because it's the reverse of how things are normally done. Typically satellite missions are driven first by the orbital and lifetime requirements, which determines the needed amount of stationkeeping fuel, which determines launch mass of the satellite, which constrains the selection of launcher and thus provider. Selection of ...


6

The report 'Resurrected DSCOVR Propulsion System – Challenges and Lessons Learned' contains a schematic of the propulsion system: and indicates thruster locations: thruster 9 and 10 are on the bottom: The thrusters were used as follows: ... the DSCOVR propulsion system, which utilizes ten 4.5 N thrusters in blowdown mode to perform Midcourse ...


6

I'm interested in any considerations to EML2 docking that are different to orbital docking. Some aspects of EML2 docking will be much easier. Some will be a bit harder. Some, we'll have to completely rethink. On the plus side, the EML2 region is much closer to flat space than is low Earth orbit. Docking will be much more intuitive. That pesky orbital ...


6

There is one wheel still operable (at least it was operable the last time they operated it), but Dawn no longer uses it. The third wheel failure was in April of this year (2017 for those reading this answer thousands of years from now). Yes, gravity tugging on the very long lever arms called solar panels is a significant driver on hydrazine usage, made much ...


6

A zillion years ago I was at a meeting where large projects were discussed and attempted to be justified. A slide was shown listing say five reasons why project such-and-such was absolutely vital and the speaker enthusiastically forwarded each reason in turn. The one response was "If you had one good reason you wouldn't need five. Ultimately it wasn't ...


6

tl;dr: I think there could be room to do this. However, I don't think a conclusive answer can be had through analyses of magnitudes on envelope-backs. A real answer would only come from even more detailed Monte Carlo calculations than those already outlined in Stationkeeping Monte Carlo Simulation for the James Webb Space Telescope. Sounds like a fun project!...


5

Here's a paper on LRO stationkeeping. The fundamental problem is articulated on page 3: LRO will fly in a mean 50 km mission orbit that, for scientific purposes, would ideally be a perfectly circular orbit. Due to the lunar non-spherical gravity, however, long term propagations of low lunar orbits show significant altitude variations and secular ...


5

Yes. In 1950 Wayne Proell proposed the use of "fuelless box-ramjets" to harness the energy of recombination of atomic oxygen at about 100 km altitude to propel space stations and satellites. (The Significance of Monatomic Gases in Planetary Space Operations, J. of Space Flight, V.2, no.7, Sept. 1950 pp.1-8, V.2, no.8, Oct.1950, pp.1-9.) In 1958 Lionel ...


5

No, unless you have a rather massive and long pole. To be in a stable orbit, your center of mass1 must be at a particular point with a particular velocity. Rearranging your own mass without expelling any will not work as you cannot move your own center of mass. However, with a long enough pole, the inverse square effects come into play, so one can change ...


5

Let's examine what Jim Bridenstine, current director of NASA and previous member of the Rocket Racing League (1, 2, 3) says. NASA Administrator Jim Bridenstine Explains the Lunar Gateway is a recording of director Bridenstine in YouTube, described as Published on Aug 7, 2018 NASA's new administrator spoke with reporters after a two-day trip to ...


5

Good question, I’m also interested if someone has a more specific answer to share! On the following table, you can find the required delta-v per year for different orbits. And about formula, I'm not sure but maybe this page can give you an idea: https://en.wikipedia.org/wiki/Delta-v


4

In this case, the terms are being used interchangeably. DISCOVR has one type of engine, i.e. the MOOG Monarc 5N thruster. DSCOVR is equipped with ten thrusters that can be used for spacecraft attitude control as well as translational maneuvers that are required for mid-course corrections and orbital adjustment maneuvers around L1. Ten thrusters are fed ...


4

What factors would make station-keeping of an Areostationary Mars satellite necessary? Mars' rather lumpy gravitational field, The Sun's gravity, Mars' two moons, solid body tides, and solar radiation pressure. That 2012 article addressed Mars' rather lumpy gravitational field (partly), but it didn't address any of those other perturbing factors. Those ...


3

I know this is quite an old post, but might be worth having a read on this paper "Efficient Orbit Propagation of Orbital Elements Using Modified Chebyshev Picard Iteration Method" by J.L. Read1, A. Bani Younes2 and J.L. Junkins3 (http://www.techscience.com/doi/10.3970/cmes.2016.111.065.pdf) Equation (7) is your inclination change. Additionally, citing ...


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