Cygnus is the second of the most commonly known ISS resupply freighters (the only more commonly used one is progress.) After cygnus launches aboard it's Antares rocket, it rendezvouses with the ISS, and is attached to the station, allowing for vital supplies to be unloaded from the noble ship and used by crewmembers. There's one flaw, one money wasting flaw, once cygnus undocks from the ISS however long later, it is sent back to earth (likely full of garbage) to burn up in the atmosphere. I've been running simulations on my phone, and I've found a few ways you can safely return a cargo ship to the earth. Currently, I only know of 2 reusable cargo ships for the ISS, the dragon 1, and the dreamchaser (in development). My question is, could you modify cygnus to be reusable? Edited: you don't have to recover the service module, just the part of the spacecraft that is actually used on the ISS (the cargo portion). This edit should make this question easier to answer.
The original proposal for Cygnus included three variants, all utilizing a common Service Module. Attached to the Service Module would be one of three different cargo modules
- Pressurized Cargo Module (PCM), aka Cygnus as we know it today.
- Unpressurized Cargo Module (UCM), for the sort of stuff cargo Dragons carry in the trunk
- Return Cargo Module (RCM), an entry capsule to, um, return cargo to Earth. This variant would have discarded the Service Module and recovered the capsule portion.
References to the RCM vanished very early on, and the UCM not long thereafter.
I do not remember if the RCM was intended to be reusable, but it would not be out of the realm of possibility. Even if the RCM had been reusable, the Service Module would still have been expended on every mission.
References (All sub-pages of Gunter's Space Page)
(for the purposes of this answer, "Cygnus" refers to the version of the vehicle that was ultimately produced, using the pressurized cargo module, and not the other variants that used the same service module.)
This can really only be start to be answered properly with an engineering study. I can't find one for Cygnus, or recall any prior attempts to make an expendable orbital spacecraft into a reusable one, except for Falcon 9 Stage 2; not finding any great authoritative resources on what the plan was or how far it got before the pivot to Starship, but Space SE discusses F9 S2 recovery here and here and perhaps elsewhere.
PearsonArtPhoto has ninja'd most of the concerns I have, both philosophical (is it really a Cygnus anymore?) and practical:
Cygnus flies to orbit inside an aerodynamic fairing (see e.g. this tweet from the NASA Landsat account, chosen because it's a relatively recent Cygnus mission) and would need to retain a (subtly different) aerodynamic shape for entry. This outer shell would also need to protect it from re-entry heating.
It's not immediately clear how it would land. To still be a Cygnus, you'd want to retain the main engine, which has been used to reboost the space station. The sides of the pressurized cargo module probably aren't good candidates for landing on; likely you'd want to land on the service module to keep the CG low. That probably means landing legs to clear the main engine bell (or attempting the scheme discussed for F9 S2 above and trying to retract the engine inside a heat shield you could splash down on). It also probably means parachutes, and finding places to put those...and good god, the engineering that goes into parachutes is completely ridiculously exceptionally difficult. As an example, the tests for CPAS (the Orion spacecraft parachutes) went on for 10 years. I know some of the people who supported that and it was exhausting work.
Cargo downmass may or may not be an option; since re-entry G loads are typically higher than launch G loads, if you want to put that reusability to work.
The Cygnus solar arrays aren't designed to be retracted, so either that capability would need to be added or the arrays would need to be releasable for entry.
Every bit of that eats into your payload upmass, which is apparently already lower than Cargo Dragon's, though Cygnus has much more pressurized cargo volume, a bigger door (CBM versus the docking adapter), and I think some more specialized payload capability to power payloads, though I'm having trouble finding a Cargo Dragon Payload User's Guide to compare to this admittedly dated Cygnus document with reasonable details about its cargo capability.
You would also likely miss out on experiments like the largest man-made fire in space and be less likely to fill the spacecraft with trash if it were expected to be landed and re-used, though I know Alice Gorman would probably adore the chance to go through discarded items from ISS and other engineers would probably leap at the chance to analyze the aftermath of a major fire in a(n otherwise empty) spacecraft if it still managed to land.
My own personal thoughts: not worth it for a spacecraft with this kind of launch tempo which launches on expendable launchers anyway. Reusability is great and kudos to SpaceX for turning public perception of it around; during my aerospace engineering education, plenty of smoke was blown about how the Shuttle program had demonstrated that reusing spacecraft was expensive and time-consuming folly. There's every reason to continue pursuing reusability, but retrofitting it doesn't make sense unless the near-future reusable spacecraft we're aware of, like Starship, don't come to be.
You could theoretically, but it'd be a lot of work, basically a new spacecraft. It'd need a heat shield, other heat protection, and the ability to fly aerodynamically. By the time all of this is taken in to account, it's a new spacecraft with a bit of resemblance to the existing one.