Cargo up and down: Dragon to demonstrate the importance of downmass

by Chris Bergin

When SpaceX’s Dragon spacecraft heads uphill at the end of the month, the young spacecraft has a long set of objectives to pass prior to being given permission to arrive at the International Space Station (ISS). However, should Dragon achieve the historic first, it will not only provide some welcome cargo, but it will have the opportunity to show off its downmass ability.

Dragon Mission C2+:

complete success of Dragon’s double set of COTS (Commercial Orbital Transportation Services) mission objectives will be extremely hard to achieve.

As such, SpaceX’s four leaf clover – once again making the mission patch (not yet confirmed to be official, but acquired via L2 documentation) – will hope to add an element of luck to Dragon’s opening objects related to the C2 elements of the mission, allowing for the flight’s progression into the complicated C3 elements associated with proximity operations, as Dragon gains the “Tally Ho” from the International Space Station.

Should Dragon negotiate the communications, positioning and abort requirements, the ultimate aim of edging ever closer to the ISS – in order for the Space Station Remote Manipulator System (SSRMS) to capture and berth Dragon to the orbital outpost – would result in a major success and a notable first, as Dragon becomes the first commercial spacecraft to arrive at Station.

Upon the completion of the nominal leak checks, hatch opening between the ISS and Dragon will not only provide yet another milestone, but also a welcome bonus for the Station’s crew, given the SpaceX vehicle will be carrying 520kg of cargo (or 460kg minus the packaging).

The manifested cargo includes Food and Crew Provisions, 306 kilograms’ worth in total, including crew meals and crew clothing.

“13 bags standard rations. Food, about 117 standard meals, and 45 low-sodium meals. 5 bags low sodium rations. Crew clothing. Pantry items (batteries, etc). SODF and Official Flight Kit,” noted the manifest, as listed under USOS (U.S. On-Orbit Segment) Cargo.

Dragon will also be carrying what is classed as Utilization Payloads, 21 kilograms worth in total, including the NanoRacks Module 9 – and ice bricks – for cooling and transfer of experiment samples for US National Laboratory.

“NanoRacks-CubeLabs Module-9 uses a 2 cube unit box for student competition investigations using 15 liquid mixing tube assemblies that function similar to commercial glow sticks. Science goals for NanoRacks-CubeLabs Module-9 range from microbial growth to water purification in microgravity,” added the manifest.

Also included in the upmass are Cargo Bags (123 kilograms), which will be repositioned for future flights. Computers and supplies (10 kilograms), such as a Laptop, batteries, power supply cables will also ride uphill with the Dragon.

None of the manifest cargo is deemed as vital to the ISS, meaning the Station will not miss out on critical items in the event Dragon is unable to arrive at the ISS.

Cargo runs in general are vital to the Station, however, not least since the end of the massive capability enjoyed by the ISS via the Space Shuttle fleet. With the orbiters now retired, an array of resupply vehicles are aiming to take up the slack, ranging from the ongoing Russian Progress vehicles, to Europe’s ATV, Japan’s HTV and – to a very small extent – the Russian Soyuz vehicles.

However, it was the additional capability of the Shuttle’s downmass role with the ISS that was often understated during the final years of their flights to the Station, something the Russian, European and Japanese resupply vehicles could not mitigate once the fleet was retired, bar the very small downmass allowed by the Soyuz.

The orbiter’s downmass ability was also wide-ranging, be it biological cargo that required sending back to Earth via the middeck, right through to large Orbital Replacement Units (ORUs) in the payload bay of the shuttle.

While Orbital’s Cygnus is aiming to join Dragon in resupplying the Station under the Commercial Resupply Services (CRS) contract, only Dragon can provide some mitigation to the downmass requirement. Should Dragon’s mission prove to be a success, this downmass ability will be demonstrated on the C2+ mission.

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Once again, none of the manifest cargo for return is classed as important, allowing Dragon an “out”, should the vehicle fail to complete the ISS leg of its mission. However, a full manifest of downmass has been revealed.

This includes items named as “Crew Preference Items”, 143 kilograms in total, downmass that will include official flight kit items.

Also included are “Utilization Payloads” – that weigh in at 93kg in total – including “Plant Signaling” hardware (16 Experiment Unique Equipment Assemblies), Shear History Extensional Rheology Experiment (SHERE) Hardware and three Materials Science Research Rack (MSRR) Sample Cartridge Assemblies.

“Plant Signaling seek: to understand the molecular mechanisms plants use to sense and respond to changes in their environment. Ambient Hardware return only; no plant sample return (24 kg),” outlined the manifest. “SHERE seeks to understand how liquid polymers behave in microgravity by measuring response to straining and stressing. Ambient hardware return; no samples (36 kg).

“MSRR experiments examined various aspects of alloy materials processing in microgravity. SETA (Solidification along a Eutectic path in Ternary Alloys-2). MICAST/CETSOL (Microstructure Formation in Casting of Technical Alloys under Diffusive and Magnetically Controlled Convective Conditions/Columnar-to-Equiaxed Transition in Solidification Processing).

Ambient hardware return with samples, coming in at 9kg, and supporting research hardware such Combustion Integrated Rack (CIR) and Active Rack Isolation (ARIS) components, double cold bags and MSG Tapes are also listed under “Utilization Payloads” for the trip down to Earth.

One interesting element of downmass relates to the return of EVA hardware, including gloves. It is not yet known if the hardware or EMU gloves – weighing in at 39kg – were used on a recent EVA, or if they are unused spares.

Also listed for return are elements of “Systems Hardware”, 345 kilogram’s worth, cargo that includes a Multifiltration Bed, Fluids Control and Pump Assembly, Iodine Compatible Water Containers and a Multiplexer belonging to the Japanese Space Agency (JAXA).

In total – again pending a fully successful mission – Dragon’s ISS demonstration flight is tasked with returning 660 kilograms of downmass, the most since the final shuttle mission with Atlantis during STS-135.

(Images: L2’s SpaceX Dragon C2/C3 Mission Special Section – Containing presentations, videos, images, interactive high level updates and more, with additional images via NASA and SpaceX). 

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