What are space tugs and who builds them?

Q: What are space tugs and who builds them?

A space tug, also called an orbital transfer vehicle (OTV) or last-mile delivery vehicle, is a small spacecraft that takes payloads from a rideshare drop-off orbit to their custom destination. Major builders include Impulse Space, Momentus, D-Orbit, Exolaunch, Launcher (now Vast), Spaceflight Inc., Atomos, and several emerging operators offering both LEO and lunar-class tugs.

Rideshare drops every payload at the same orbit. A space tug picks up from there, propelling individual satellites to the orbital plane, altitude, or destination they actually need. The category emerged in the late 2010s as smallsat operators wanted custom orbits without paying for dedicated launches.

What space tugs do

Three jobs dominate:

Phase / plane changes: drop a constellation member into its station-keeping slot
Altitude raises: push from a low rideshare drop-off (e.g., 525 km SSO) up to an operating altitude (e.g., 580 km)
Geostationary transfer and beyond: Earth-Moon transfers, geo-final-mile, escape trajectories for cis-lunar payloads

Tugs vary by propulsion type: chemical (high thrust, fast manoeuvres, more propellant), electric (slow, fuel-efficient), or hybrid.

The major operators

LEO and mid-Earth tugs:

Impulse Space: Mira (chemical) for fast LEO/MEO transfers
Momentus: Vigoride (water plasma); has flown multiple LEO missions
D-Orbit: ION Satellite Carrier, the most-flown commercial OTV by count
Exolaunch: Reliant transfer vehicle alongside its rideshare brokerage
Spaceflight Inc.: Sherpa series (Sherpa-LTC, Sherpa-LTE)
Atomos Space: solar-electric tug aimed at GEO and beyond

GEO and cis-lunar:

Impulse Space Helios: high-energy upper stage for GEO direct
Quantum Space: Ranger, cis-lunar
Astroscale and ClearSpace: overlapping into in-orbit servicing
Blue Origin Blue Ring: multi-tonne tug for GEO and lunar transfer

Why the category matters

Without tugs, commercial rideshare hits a ceiling. Constellation operators that want planes spread across 20° of right ascension can’t do that economically from a single rideshare. Tugs let one launch serve many destination orbits, a force multiplier for cadence-constrained smallsat operators.

Government interest is rising. The Space Force and Space Development Agency increasingly contract OTV services for tactically responsive launch and rapid relocation; NASA buys cis-lunar delivery for Artemis support.

For the live list of OTV builders and operators, see /tags/space-tugs.