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Space tug

Space tug is a science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Space tug rather than just read about it. In short: A space tug is a type of spacecraft used to transfer spaceborne cargo from one orbit to another orbit with different energy characteristics. The term can include expendable upper stages or spacecraft that are not necessarily a part of their launch vehicle.

Space tug — main illustration
Space tug — illustration

Key takeaways

  • Space tug belongs to science; place it in that map before memorising details.
  • Learn the definition first, then one example that makes the definition concrete.
  • Connect Space tug to a quantity you can measure, compute or draw — that is where exam questions come from.
  • Reproduce the core statement of Space tug from memory before moving on to harder problems.

Reference excerpt

A space tug is a type of spacecraft used to transfer spaceborne cargo from one orbit to another orbit with different energy characteristics. The term can include expendable upper stages or spacecraft that are not necessarily a part of their launch vehicle. However, it can also refer to a spacecraft that transports payload already in space to another location in outer space, such as in the Space Transportation System concept. An example would be moving a spacecraft from a low Earth orbit (LEO) to a higher-energy orbit like a geostationary transfer orbit, a lunar transfer, or an escape trajectory. The term is often used to refer to reusable, space-based vehicles. Some previously proposed or built space tugs include the NASA 1970s STS proposal or the proposed Russian Parom, and has sometimes been used to refer to expendable upper stages, such as Fregat, Spaceflight Industries Sherpa, and the Inertial Upper Stage, when such stages are optional.

Background The space tug was first envisioned in the post-World War II era as a support vehicle for a permanent, Earth-orbiting space station. It was used by science fiction writer Murray Leinster as the title of a novel published in 1953 as the sequel to Space Platform, another novel about such a space station.

Existing space tugs Space tugs can be roughly categorised into a few types:

Large tugs that dock with satellites in orbit which may be able to perform services like refuelling or repairs or enhancements as well as changing the satellites orbit whether that is to extend life of satellite or to deorbit it. Optional rocket kick stages used to place some payloads into higher orbits. An example would be Photon Satellite Bus but this might just be considered part of the rocket system rather than a space tug and this article does not really consider these in detail. Smaller tugs that are mainly cubesat deployers with some propulsion to deploy the cubesats to different orbits.

Large tugs that dock

Mission Extension Vehicle

In 2011 ViviSat a joint project between U.S. Space and ATK proposed the Mission Extension Vehicle. In 2016 ViviSat was dissolved when U.S. Space declared bankruptcy and ATK merged with Orbital Science Corporation to form Orbital ATK. In 2017 Orbital ATK got the go ahead from the FCC to begin development of the spacecraft with new partner Northrop Grumman who was developing a tug of their own. In June 2018, both companies pooled their resources and merged to form a new company called Northrop Grumman Innovation Systems. On October 9, 2019, the first of these tugs MEV-1 was launched from Baikonur Cosmodrome in Kazakhstan on a Proton-M rocket. In February 2020, MEV-1 successfully docked with Intelsat 901 and returned it to geosynchronous orbit, allowing it to continue operating 4 years past its service life. MEV-1 will continue to maintain this position for a 5-year period, after which it will move the satellite back into a graveyard orbit for retirement. MEV-2 was launched August 15, 2020, with Galaxy 30 on an Ariane 5 to perform a similar maneuver with Intelsat-1002.

Shijian-21 In December 2021 - January 2022, China's Shijian-21 space debris mitigation satellite has docked with the defunct Beidou-2 G2 navigation satellite to drastically alter its geostationary orbit, demonstrating capabilities only previously exhibited by the United States.

Smaller tugs and dispensers

SHERPA

Spaceflight Inc. developed SHERPA, which builds upon the capabilities of the Spaceflight Secondary Payload System (SSPS) by incorporating propulsion and power generation subsystems, which creates a propulsive tug dedicated to maneuvering to an optimal orbit to place secondary and hosted payloads. The maiden flight of two separate unpropelled variants of the dispenser was in December 2018 on a Falcon 9 rocket. This flight deployed 64 small satellites from 17 countries.

ION Satellite Carrier D-Orbit, an Italian space logistics and transportation company, developed the InOrbit NOW ION Satellite Carrier. The first launch occurred on September 3, 2020, on a Vega rocket, but subsequent launches have all been on SpaceX Falcon 9 Transporter missions. On January 3, 2023, the company launched its seventh and eighth vehicles, Second star to the right, aboard the SpaceX Transporter-6 Mission.

Long Duration Propulsive ESPA (LDPE)

LDPE is based on a Northrop Grumman payload adapter used to help attach the upper stage to the main satellite in addition to hosting a few slots for other smallsats. However, the entire system is powered by the ESPAStar satellite bus, which is in charge of power consumption and distribution as well as propulsion making it a fully operational space tug capable of deploying different payloads at different orbits. ESPAStar has the capability to host 6 smallsat payloads totaling 1,920 kg (4,230 lb). The system is also able to provide 400 meters per second of delta-V via a Hydrazine propulsion module. The first LDPE was launched on December 7, 2021, on an Atlas V rocket as part of the STP-3 mission. The second launch was on November 1, 2022, on a Falcon Heavy rocket as part of the USSF-44 mission. A third mission was on January 15, 2023, on USSF-67 mission.

Vigoride by Momentus Space

Momentus Space develops different space tug versions focusing on large velocity changes over 1 km/s. Two demonstration missions of their Vigoride platform took place on May 25, 2022, and January 3, 2023 with key tests occurring through 2022. Momentus Space became widely known in October 2020 when it reached a SPAC investment deal with Stable Road Acquisition Corp valuing the combined entity at over $1 billion.

Epic Aerospace Epic Aerospace's Chimera LEO 1 launched on January 3, 2023.

Launcher Reports surfaced circa June 15, 2021, of Launcher's Orbiter space tug. Launching on its own rocket as well as SpaceX’s Falcon 9 it provides 150 kilograms of payload, either 90 units of CubeSat or else larger satellites using standard smallsat separation systems. With a chemical propulsion system using ethylene and nitrous oxide propellants it is capable of 500 meters per second of delta-v, more with additional propellant tanks. Orbiter SN1 launched on January 3, 2023. After Launcher was acquired by VAST, the Orbiter program was cancelled.

… excerpt ends here. Continue reading the full article.

Illustrations

Space tug: Reusable, modular 1969 NASA vision Space Tug (canceled)
Reusable, modular 1969 NASA vision Space Tug (canceled)
Space tug: The Jupiter bound Galileo spacecraft and its attached Inertial Upper Stage (IUS) being deployed after being launched by the Space Shuttle Atlantis on the STS-34 mission. The IUS was an optional payload for missions where the Space Shuttle was used to take a payload beyond Low Earth Orbit. By contrast, the Space Shuttle external tank was always included and used whenever a shuttle launch took place.
The Jupiter bound Galileo spacecraft and its attached Inertial Upper Stage (IUS) being deployed after being launched by the Space Shuttle Atlantis on the STS-34 mission. The IUS was an optional payload for missions where the Space Shuttle was used to take a payload beyond Low Earth Orbit. By contrast, the Space Shuttle external tank was always included and used whenever a shuttle launch took place.
Space tug: Space Tug crew module concept
Space Tug crew module concept

Worked examples

Example 1 — a first encounter with Space tug

Start with the simplest possible case. Write down what Space tug claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Space tug before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Space tug ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Space tug

In research
Space tug appears in science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry
Engineering practice reuses Space tug in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom
Space tug is common in secondary-school and first-year university syllabi. It links to neighbouring topics Space tugs, Spacecraft, Spacecraft propulsion, so understanding it makes those chapters shorter.
In everyday life
Look for Space tug outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

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How to study Space tug in 20 minutes

  1. Read the reference excerpt below once, without taking notes.
  2. Close the page and write down what Space tug means in your own words.
  3. Compare your version with the excerpt and mark what you missed.
  4. Work through the three examples above with pen and paper.
  5. Explain Space tug out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Space tug in simple terms?

A space tug is a type of spacecraft used to transfer spaceborne cargo from one orbit to another orbit with different energy characteristics. The term can include expendable upper stages or spacecraft that are not necessarily a part of their launch vehicle.

Why does Space tug matter?

Because it connects several science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Space tug?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Space tug.

Tags

  • Space tugs
  • Spacecraft
  • Spacecraft propulsion

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