The International Space Station (ISS) is due to be retired
and de-orbited sometime during 2030. It
replacements are very likely to be commercial stations. The question arises: in what orbit should these new space
stations be located?
This is an important question, because they will all be located in one or
another low circular Earth orbit (LEO), in
order to stay out of the Van Allen Belt radiation (roughly about 900 miles = 1400
km up). Plane changes in low circular
Earth orbit are very costly to achieve, in terms of rocket delta-velocity (dV)
requirements.
This is because the plane change dV requirement (direction
only, with no speed change) is dV =
2*V*sin(angle change/2). At typical LEO
speed (around 7.8 km/s), a 10 degree plane
change costs about dV = 1.36 km/s. A 20
degree change costs 2.7 km/s. A 30
degree plane change costs about 4.0 km/s.
It gets worse very quickly, the
bigger the plane change angle.
The “right” answer to this important question depends
upon what you really intend to do with these new space stations. If you want them to support human or robotic missions
to the moon and planets, the ISS
orbit is just flat wrong, and by
a large amount!
Such missions need to be flown from an orbit near the plane of the moon’s orbit, or the planes of the orbits of the planets. All the planes of the various planets’ orbits about the sun are rather close to the plane of the Earth’s orbit about the sun, called the “ecliptic plane”. This situation is illustrated in the figure.
All these possible destinations do not require large
plane changes, if mounted from Earth orbits
inclined somewhere close to a band between the Earth’s orbital plane and the
ecliptic plane, a band that also
contains the orbit of the moon about the Earth.
The plane of the ISS is at 55 degrees inclination to the
Earth’s equator, set there to enable
easy access for the Russians from launch sites in Russia. That’s a 60+ degree plane change to go
elsewhere, at least dV = 7.8 km/s! Earth surface escape is only 11 km/s!
That high ISS inclination is just plain wrong for
easy access to the moon or planets.
It always was. An equatorial
orbit about the Earth has the very lowest velocity requirements to reach from
an equatorial launch site, but all the
orbits in the equatorial-to-ecliptic band are fairly easy to reach, from pretty much any launch site in the US.
So, if you really want these future space
stations to actually successfully support future missions to the moon and
planets, manned or robotic, you want them to be in this band of
low-inclination orbits about the Earth.
Simple as that!
What might such mission support be? Well,
perhaps assembly by docking together a lunar or
interplanetary craft, at a space station
using remote manipulator arms, from components
sent up from Earth. This is an approach
well documented by the experience of building the ISS from the Space Shuttle
with its arm, and by the experience ever
since of using the ISS arm to dock supply and crew vehicles.
These lunar or interplanetary craft could be fueled
for their missions, using propellants previously
sent up by tanker vehicles from Earth,
and kept in tanks at the space station for such a purpose. We would need a way to load and unload
cryogenic propellants for this job,
since many such craft will need them. So far,
only room temperature storable propellants have been transferred in
weightlessness, using expulsion bladders
inside the tanks. You cannot do that
with cryogenics! No materials have
the necessary very large elongation capabilities, at such low temperatures!
SpaceX wants to do this tanker vehicle transfer with cryogenic
oxygen and methane in their “Starship” soon,
using ullage thrust. That approach
does alter the orbit, something not
tolerable when operating at a space station.
But there might be an easy way to do that cryogenic transfer
job, without spinning huge vehicles, or without applying any ullage thrust that
alters their orbits. See the
article “Tank Design for Easy Cryogenic Transfers In Weightlessness”, posted 26 July 2025 to this site (search code:
26072025, search keyword: space program). As the article indicates, this concept is undergoing the patent process. A patent is pending.
You
turn the system on, wait several
seconds, then start the propellant
transfer pump. No ullage thrust gets
applied, and no vehicles or space
station are spun up. There are no unwanted
forces at the tank mountings, applied to
anything!
The notion of elliptic departure and capture was explored in
the posting “Elliptic Capture”, dated 1
October 2024 this site. The notion of space
tug assist was first explored in the article “Tug-Assisted Arrivals and Departures”, dated 1 December 2024 this site. The search codes for those articles are
01102024 and 01122024, respectively. Both share the search keyword “space program”.
This selection of proper space station orbits, an effective cryogenic propellant transfer
tank, the notion of elliptic orbit departure
and arrival, and a reusable space tug
stage, together make possible a space
program of cost effectiveness that dwarfs anything ever seen before! And THOSE FOUR THINGS are what really needs
to happen!
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Search code DDMMYYYY 11112025
Search keyword space
program
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