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For GW Johnson re Artemis II Space Tug concept....
The Interim Upper Stage is cryogenic .... it is intended to be used immediately after the first stage falls away, and I'll bet the mission plan calls for nearly continuous use until fuel is exhausted, at which point the Orion capsule and service module would be on their way.
The Space Tug concept would require Interim Upper 'Stage to hold onto it's cryogenic propellants for several days, so it can be used to decelerate as the vehicle approaches Earth.
The threat of boil off can can be addressed with sun shades, but those are not part of the current mission plan.
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For GW Johnson re Starship as possible Space Tug for Artemis II
https://www.google.com/url?sa=i&url=htt … AdAAAAABAE
If the link above works, it will show a side view of the funnel shaped adapter that is needed to allow use of the 5 meter diameter Interim Second Stage.
The Space Tug will need the same adapter to dock with the Interim Second Stage, adapted for the Starship diameter.
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Could be a simple bar truss. The Russians did a lot of those. Bars shipped up as bundles in payload bays, then snapped together in space by means of appropriate snap joints.
But you still need a way to refuel the Interim Upper Stage (IUS) on-orbit, before it departs to send the cluster to the moon. Why? Bigger cluster. It needs more dV than it has left after reaching LEO, in order to put an Orion/service module (and maybe a small lander) into low lunar polar orbit. The service module can get Orion back onto the trip home, from that low lunar orbit, but it cannot get both into and back out of low lunar orbit. It is too small.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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GW Johnson notified me by email that an article about Space Tugs is now available at his exrocketman blog site:
https://exrocketman.blogspot.com/
NewMars members should have no difficulty following the presentation.
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This one was posted on-line for the forums before I put it up on "exrocketman". The two differ only in some minor wordsmithing here and there.
GW
GW Johnson
McGregor, Texas
"There is nothing as expensive as a dead crew, especially one dead from a bad management decision"
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For GW Johnson ....
If you have time, please think about the interface between the Space Tug and a 5000 ton deep space vessel.
I have started a 3D Printer project to create a model of a Large Ship with dual counter rotating habitat rings, and I have chosen the arbitrary mass of 5000 as a design goal. As you know, this figure came out of the two years of work RobertDyck put into his Large Ship concept.
The design of the deep space vessel must allow for distribution of force from the Space Tug interface, so I expect we'll end up with at least three compression force pathways, and perhaps four for bilateral symmetry. I am planning to make nose and stern mirror images of each other, so the deep space vessel does not need to rotate to work with the Space Tug at either departure or arrival.
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A UK firm is (apparently) thinking about using a fusion device to propel a space tug...
URL here: https://interestingengineering.com/inno … time-by-50
Sunbird: Nuclear fusion rocket by UK firm could cut Mars travel time by 50%
Scientists have toyed with the idea of nuclear rockets since the 1950s. Will they finally become a reality?Updated: Mar 07, 2025 10:10 AM EST
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Chris Young9 hours ago
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Sunbird: Nuclear fusion rocket by UK firm could cut Mars travel time by 50%
An artist's impression of Sunbird.Pulsar Fusion
UK startup Pulsar Fusion just revealed a nuclear fusion-powered rocket that could halve travel time across the solar system.
The spacecraft, called ‘Sunbird’, is designed to remain in orbit for quick deployment. It attaches to larger rockets, speeding them to distant worlds in a fraction of the time.
On its website, Pulsar Fusion claims Sunbird can fly 1000–2000 kg of commercial cargo to Mars in roughly four months.
Meet ‘Sunbird’
Pulsar Fusion’s Sunbird spacecraft acts somewhat like a space tug. In a concept video shared on the company’s website, Sunbird can be seen attaching to a Starship-like rocket before powering it to Mars.Using existing technologies, NASA estimates it would take seven to eight months for a rocket such as Starship to reach Mars. According to Pulsar Fusion, its new spacecraft could cut this travel time dramatically.
The company claims it could propel a spacecraft with a mass of about 1,000kg (2,200lb) to Pluto in four years. As a point of reference, NASA’s New Horizon spacecraft took roughly eight years to reach the distant planet. Using Sunbird for an Earth to Saturn mission would take approximately two years, according to the firm. A trip to Mars, meanwhile, would take as little as four months.
Sunbird is powered by Pulsar Fusion’s in-development Duel Direct Fusion Drive (DDFD). This is a compact nuclear fusion engine that provides thrust and power. According to the information available on Pulsar Fusion’s website, DDFD provides a specific impulse of 10,000–15,000 s and 2 MW of power. When fired up, it would temporarily become the hottest place in the solar system, producing exhaust speeds of more than 500,000mph (804,672km/h).
Pulsar Fusion started developing the engine in 2023 at its headquarters in Milton Keynes, UK. Static tests are set to “begin in 2025 followed by an In Orbit Demonstration (IOD) of the core technology components in 2027”.
Are nuclear rockets the future of space travel?
Scientists and engineers have floated the idea of nuclear rockets around since the 1950s. They would roughly double the efficiency of traditional chemical rockets while delivering much higher thrust than ion propulsion systems.Cutting down travel time is an incredibly important goal for the space industry. Lower travel times are crucial for astronaut health due to higher exposure to cosmic radiation during transit.
Historically, though, the issue with nuclear propulsion has been the funding required to develop these advanced systems. Long-term development has often been cut short due to budget cuts. These have led NASA to focus on programs that would provide a faster return on their investment.
NASA’s NERVA program, for example, was cut in 1973, despite promising results. It was cut due to budget cutbacks and a call to focus on the Space Shuttle program.
In a 2023 interview with IE, former NASA astronaut and Ad Astra founder Franklin Chang Diaz said funding was the main stumbling block to sending his nuclear electric propulsion engine to orbit. “The technology is there,” he explained, “[but] the timeline for when we’ll see a VASIMR demonstration in space is all dependent on the funding.”
Pulsar Fusion is collaborating with the Universities of Cambridge and Southampton, as well as the Nuclear Advanced Manufacturing Research Centre (AMRC). In 2022, the company secured funding from the UK Space Agency.
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Chris Young Chris Young is a journalist, copywriter, blogger and tech geek at heart who’s reported on the likes of the Mobile World Congress, written for Lifehack, The Culture Trip, Flydoscope and some of the world’s biggest tech companies, including NEC and Thales, about robots, satellites and other world-changing innovations.
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Update ahead of Google Meeting for Sunday 2025/04/06
If by chance we are unable to implement a steering function for the Solar Propulsion version of the Space Tug, it would be possible to make the docking adapter able to accept variable input to the payload vessel, using a docking adapter able to adjust the angle of thrust to pass through the CG of the client vessel.
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