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Comment by westurner | Hacker News Reader

I wonder if the ISS could instead be scrapped to the moon.

Let's get this space station to the moon.

Can a [Falcon 9 [Heavy] or similar] rocket shove the ISS from its current attitude into an Earth-Moon orbit with or without orbital refuelling?

The ISS weighs 900,000 lbs on Earth.

Have we yet altered the orbital trajectory of anything that heavy in space?

Can any existing rocket program rendezvous and boost sideways to alter the trajectory of NEOs (Near-Earth Objects) or aging, heirloom, defunct space stations?

Which of the things of ISS that we have internationally paid to loft into orbit would be useful for future robot, human, and emergency operations on the Moon?

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NASA evaluated a bunch of options before deciding to de-orbit ISS. You can read a summary here: https://www.nasa.gov/wp-content/uploads/2024/06/iss-deorbit-... (PDF)

About boosting to a higher orbit, they wrote:

"Space station operations require a full-time crew to operate, and as such, an inability to keep crews onboard would rule out operating at higher altitudes. The cargo and crew vehicles that service the space station are designed and optimized for its current 257 mile (415km) altitude and, while the ability of these vehicles varies, NASA’s ability to maintain crew on the space station at significantly higher altitudes would be severely impacted or even impossible with the current fleet. This includes the International crew and cargo fleet, as Russian assets providing propulsion and attitude control need to remain operational through the boost phase.

"Ignoring the requirement of keeping crew onboard, NASA evaluated orbits above the present orbital regime that could extend just the orbital lifetime of the space station. [...]

"However, ascending to these orbits would require the development of new propulsive and tanker vehicles that do not currently exist. While still currently in development, vehicles such as the SpaceX Starship are being designed to deliver significant amounts of cargo to these orbits; however, there are prohibitive engineering challenges with docking such a large vehicle to the space station and being able to use its thrusters while remaining within space station structural margins. Other vehicles would require both new certifications to fly at higher altitudes and multiple flights to deliver propellant.

"The other major consideration when going to a higher altitude is the orbital debris regime at each specified locale. The risk of a penetrating or catastrophic impact to space station (i.e., that could fragment the vehicle) increases drastically above 257miles (415km). While higher altitudes provide a longer theoretical orbital life, the mean time between an impact event decreases from ~51 years at the current operational altitude to less than four years at a 497 mile (800km), ~700-year orbit. This means that the likelihood of an impact leaving station unable to maneuver or react to future threats, or even a significant impact resulting in complete fragmentation, is unacceptably high. NASA has estimated that such an impact could permanently degrade or even eliminate access to LEO for centuries."

Thanks for the research.

How are any lunar orbital trajectories relatively safe given the same risks to all crafts at such altitudes?

Is it mass or thrust, or failure to plan something better than inconsiderately decommissioning into the atmosphere and ocean.

If there are escape windows to the moon for other programs, how are there no escape windows to the moon for the ISS?

Given the standing risks of existing orbital debris and higher-altitude orbits' lack of shielding, are NEO impact collisions with e.g. hypersonic glide delivery vehicles advisable methods for NEO avoidance?

The NEO avoidance need is still to safely rendezvous and shove things headed for earth orbit into a different trajectory;

Is there a better plan than blowing a NEO up into fragments still headed for earth, like rendezvousing and shoving to the side?

m_ISS ~ 4.5e5 kg [1]

Rocket equation [2]:

m_0 = m_f exp(v_delta / v_e)

where

m_f = final mass, i.e. mass of ISS and the boosters

m_0 = m_f + propellant mass

v_delta = velocity change

v_e = effective exhaust velocity of the boosters

Let's try a high-thrust transfer from LEO to the Lunar Gateway's orbit via TLI (Trans-Lunar Injection) [3]:

v_delta = 3.20 + 0.43 = 3.63 km/s

For boosters, let's use the dual-engine Centaur III (because Wikipedia has mass and v_e data for it) [4]:

m_dry = 2462 kg

m_propellant = 20830 kg

v_e = 4.418 km/s

The idea is to attach n of these to the ISS. The rocket equation becomes

m_ISS + n (m_dry + m_propellant) = (m_ISS + n m_dry) exp(v_delta / v_e)

Solve for n:

n = m_ISS (exp(v_delta / v_e) - 1) / (m_propellant + m_dry (1 - exp(v_delta / v_e)) )

Plug in numbers and find

n ~ 32.4

So we need 33 Centaur III (and some way to attach them, which I optimistically assume won't add significantly to the ISS mass).

Total Centaur III + propellant mass: 33 * (2462 + 20830) = 768636 kg

Planned Starship payload capacity to LEO is 2e5 kg [5], so assuming that a way can be found to fit 7 Centaur III in its payload bay, we can get all 33 boosters to LEO with five Starship launches.

Why not use Starship itself? Its Raptor Vacuum engines have lower v_e (~3.7 km/s) [6], and if you want it back, you need to add fuel for the return trip to m_f. Exercise for the reader!

[1] https://en.wikipedia.org/wiki/International_Space_Station

[2] https://en.wikipedia.org/wiki/Tsiolkovsky_rocket_equation

[3] https://en.wikipedia.org/wiki/Delta-v_budget#Earth_Lunar_Gat...

[4] https://en.wikipedia.org/wiki/Centaur_(rocket_stage)

[5] https://en.wikipedia.org/wiki/SpaceX_Starship_(spacecraft)

[6] https://en.wikipedia.org/wiki/SpaceX_Raptor#Raptor_Vacuum

Thanks for the numbers. I think it's still possible to create gists with .ipynb Jupyter notebooks which have can have latex math and code with test assertions; symbolic algebra with sympy, astropy, GIZMO-public, spiceypy

> and some way to attach them

Because of my love for old kitchens on the Moon.

(The cost then to put all of that into orbit, in today's dollars)

So, orbitally refuelling Starship(s) would be less efficient than 33 of the cited capability all at once.

This list is pretty short:

Template:Engine_thrust_to_weight_table: https://en.wikipedia.org/wiki/Template:Engine_thrust_to_weig...

What about solar; could any solar-powered thrusters - given an unlimited amount of time - shove the ISS into a dangerous orbit towards the moon instead of the ocean?

> and some way to attach them

There's a laser welding in space spec and grants FWIU.

Can any space program do robotic spacecraft hull repair in orbit, like R2D2? With laser welding?

Or do we need to find more people like Col. McBride in brad pitt space movie, more astronauts?

Is the task to fabricate a 3d mount to attach a gradual thrust mechanism to a NEO?

> sympy, astropy, GIZMO-public, spiceypy

poliastro

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