Why the heck are they launching from Alaska? Polar orbit? Something else? If I understand correctly, being as close as you can to the equator gives you more ‘throw’ toward orbit. No?
Yep, high-inclination (polar) orbits only. And a likely focus on sun-synchronous orbits, which are friendly to smallsats for various reasons.
It’s not just throw–you basically can’t launch at all to inclinations below your latitude. That would require significant extra delta V (a “plane change”). But launching to inclinations above your latitude is easy enough. And at very high inclinations it basically doesn’t matter at all where you are.
@Dr.Strangelove:
Absent more context that headline sure sounds like they lost a launch vehicle with 5 crewmen on board.
Which makes the subhead “It’s a really nice Christmas present for the team.” pretty jarring.
The fact the first half of the article wasn’t even talking about this launch, but rather one back in September was further confusing. And that the CEO’s quote about Christmas presents was made before the launch and was assuming they’d have a success. By those lights, what actually happened was more like finding coal in your stocking.
Good info, & thanks for the link, but whoever wrote that article sux as a writer. Ars Technica usually does better than that.
To fill in a smidgen of background on what the good Dr. almost said …
Being closer to the equator gives you more velocity eastward. Being at the equator gives you the most velocity eastward.
If you’re trying to go east, then every bit you can get from your launch location is that much less you need to get through fuel. It’s “free” velocity, which all else equal leaves more weight for payload. As you say.
But if you’re not trying to go eastward, or not much, then closeness to the equator may be unnecessary or actively harmful versus the trajectory you do want.
How does it compare with John Glenn’s suborbital flight?
Some graphics, while we’re at it. There are many different types of orbits, some very unusual, but the ground track for a generic low-Earth orbit usually looks something like this:
Note that it’s roughly sine-wave shaped, though it doesn’t quite line up after one cycle. The inclination of this orbit is the maximum latitude that the ground track reaches.
To have any hope of an efficient launch, your launch facility has to be below some point on the ground track. If you’re shifted east or west, that’s ok–you can either wait for the ground track to itself shift, or do your own shift in orbit (this is fairly cheap, propellant-wise). But it doesn’t matter how long you wait if your launch facility is too far north or south.
Beyond this, though, you can get a little boost from the Earth’s rotation. A LSLGuy noted, that’s just free velocity, around 460 m/s. Out of the ~9000 m/s you need, that’s not a ton, but every bit helps.
Farther north or south, the velocity drops (shorter distance to Earth’s axis of rotation), though some of that is made up by virtue of vector math effects–the velocity vector is better lined up with the orbit. But the equator is still better.
A near-polar orbit track looks like this, though:
At the equator, the ground track is near-vertical. And the slight angle is actually westward, so Earth’s rotation is actually working against you, though not by much (due to the aforementioned vector math effects).
If you’re targeting polar orbits, then, there’s really no harm in being at a high latitude. Earth imaging sats in particular like sun-synchronous orbits due to the high level of coverage with good illumination.
It may not be a lot, but because of the rocket equation, your extra fuel needed on the pad would be more significant than the number alone would imply.
Quite true. Under some conditions, it could be the difference between achieving orbit vs. not. At the very least there will be a highly disproportionate effect on payload.
OK, super naive question:
Once you’re in an equatorial orbit, wouldn’t it be cheap to spin the orbit around the axis formed by the perigee/apogee by applying thrust at 90 degrees to the orbit halfway between perigee/apogee? The orbit would start to (I don’t know if this is the right word) precess around the long axis, spinning slowly. Once you get to (say) 90 degrees along this precession, apply an opposite thrust to stop the precession. It seems like you could go from equatorial to polar in this fashion
I’m sure I’m not expressing myself well, but picture a penny hanging from a string. The penny is a circular (yes, elliptical IRL) orbit with the apogee, perigee at top/bottom. Now give the penny a small shove on the left or right and it slowly rotates about the axis defined by perigee / apogee. When the orbit has rotated enough, give it a small flick the other direction, now you’ve changed the orbit to a different-ish plane.
Obviously you’d have to thrust exactly halfway between perigee/apogee, which may be a brief moment, but you could either let the orbit precess very slowly to the desired plane, or apply thrust repeatedly at that correct moment to rotate the orbit more quickly, and do the same at the end of the cycle.
I’ve tried finding an answer to this, but all the references I pull up discuss going from a higher to lower orbit or transferring Hohman-like to another orbit, rather than discussing rotating an orbit along a different axis.
You can certainly change your inclination, even enough to flip. But it would take more dV than even the extra fuel on the pad to make up for the 460m/s Dr.Strangelove mentioned, and you have to carry this extra fuel all the way up.
But once you’ve started the orbit rotating around it’s long axis, you can let it precess as slowly as you like. Let it take months if you wish and don’t have the fuel. It’ll rotate forever until you stop it with the same amount of dV, however small.
Under almost all conditions, that would be very, very expensive.
Consider a low, circular, equatorial orbit. The velocity vector is 8000 m/s east, and you want to convert that to 8000 m/s north. The vector sum of those is 11,300 m/s! That’s the delta-V you need to expend.
You seem to be imagining that the orbit itself has a kind of momentum, so that you just have to start the rotation, but that’s just not the way things work. There are maneuvers that sorta work like that–for example, changing the phase of an orbit involves raising/lowering your orbit slightly, just kinda drifting into the right orbit, and then lowering/raising it again. But that doesn’t work for inclination changes.
The one case where plane changes like that are not too expensive is for highly elliptical orbits. If your apogee is high enough, the velocity at that point is not very high–zero, in the limiting case. And so if you maneuver there, then the delta-V requirements are not so great. If you absolutely had to change your plane, then it’s likely better to raise your apogee, do the maneuver, then lower it again. But most satellites don’t have nearly enough delta-V to do that, either, so it’s a moot point.
I highly recommend Kerbal Space Program for gaining intuition for all this stuff!
Wooden satellites now:
Are you sure it is NASA’s plan? If I am not mistaken SpaceX company is going to colonize Mars by setting there the modules for life.
Whoops I had meant to write “the moon” there!
NASA has chosen four small-scale astrophysics missions for further concept development in a new program called Pioneers. Through small satellites and scientific balloons, these selections enable new platforms for exploring cosmic phenomena such as galaxy evolution, exoplanets, high-energy neutrinos, and neutron star mergers.
…
These are the four concepts chosen for further study:Aspera is a SmallSat that will study galaxy evolution. Through observations in ultraviolet light, it will examine hot gas in the space between galaxies, called the intergalactic medium, and the inflow and outflow of gas from galaxies. The intergalactic medium is a major component of the universe, but is poorly measured; Aspera would close this gap. The principal investigator is Carlos Vargas at the University of Arizona.
Pandora is a SmallSat that will study 20 stars and their 39 exoplanets in visible and infrared light. It is aimed at disentangling the signals from stars and planetary atmospheres. Understanding how changes in starlight affects measurements of exoplanets is an outstanding problem in the search for habitable planets beyond the solar system. The principal investigator is Elisa Quintana of NASA Goddard Space Flight Center.
StarBurst is a SmallSat that will detect high-energy gamma rays from events such as the mergers of dense stellar remnants called neutron stars. This would provide valuable insight into such events, which are also detected through gravitational waves by observatories on Earth. These events are where most of the heavy metals in the universe, such as gold and platinum, are formed. To date, only one such event has been observed simultaneously in gravitational waves and gamma-rays; StarBurst would find up to 10 per year. The principal investigator is Daniel Kocevski of NASA Marshall Space Flight Center.
PUEO is a balloon mission designed to launch from Antarctica that will detect signals from ultra-high energy neutrinos, particles that contain valuable clues about the highest energy astrophysical processes, including the creation of black holes and neutron star mergers. Neutrinos travel across the universe undisturbed, carrying information about events billions of light years away. PUEO would be the most sensitive survey of cosmic ultra-high energy neutrinos ever conducted. The principal investigator is Abigail Vieregg of the University of Chicago.
The Europa Clipper (EC) probe is no longer required to launch on SLS:
Congress had made it a requirement to launch EC on SLS, since it was one of the few ongoing reasons for the existence of SLS. But SLS is late, expensive, and due to its solid fuel boosters, may be such a rough ride to orbit that it damages the probe.
Falcon Heavy does not have as much oomph as SLS, but it is capable of launching EC with an extra gravity assist maneuver. Or–with some fairly involved development–it could launch a Centaur upper stage with EC on top. The latter is not that likely IMO, but a standard launch, plus off-the-shelf kick stage, and a slightly longer transit time sounds perfectly reasonable to me. And much, much cheaper.
I didn’t know a space station was being built to orbit the moon.
See your own post #18 in this thread.
Ah yes! I thought that was just for the duration of the lunar landing mission (and I hadn’t memorised the name so didn’t draw a link between that and this).
Mind you, it’s not clear from the Guardian link how permanent the lunar Gateway will be. It seems unclear from its Wikipedia entry, except for this bit which suggests a sort of permanence:
Gateway will be the first mini-space station to be both human-rated, and autonomously operating most of the time in its early years, as well as being the first deep-space station, far from Low Earth orbit. This will be enabled by more sophisticated executive control software than on any prior space station, which will monitor and control all systems.
Note the ‘autonomous’ keyword. A station in lunar orbit is quite dangerous from a habitation standpoint, as unlike the ISS a solar storm would kill any inhabitants, so as I understand it the station will be normally uninhabited (autonomous) except during a mission. It’s basically a fuel dump, and reading that wiki article, a pretty useless one.