News SLS EM-3 to Deploy Deep Space Gateway's Hab Module

[Nicholas Kang]

The EM-3 flight has gained its first notional mission outline, detailing a flight to Near-Rectilinear Halo Orbit to deploy the Hab module for the new Deep Space Gateway.

According to the preliminary mission outline, the EM-3 flight would be a crewed mission to Near-Rectilinear Halo Orbit (NRHO) around the Moon. Placing the DSG in a NRHO will create a DSG orbital trajectory that takes the outpost close to the lunar surface to permit low-energy transfer opportunities for scientific excursions in cislunar space and to the lunar surface itself.

For EM-3 specifically, the mission carries a total duration of 16-26 days with baseline objectives to “demonstrate spacecraft systems performance beyond LEO for crewed flight” and to launch the DSG habitat module to NRHO and mate the Hab to the already-launched Power and Propulsion Element (PPE).

The PPE will have been launched on the previous SLS mission, EM-2.

To accomplish these objectives, both the crewed Orion module and the Hab element for the DSG will launch atop an SLS Block 1B rocket as co-manifested payloads from the Kennedy Space Center, Florida.

SLS will launch into a 28.5 degree inclination orbit, with SLS’s SRBs and Core Stage inserting Orion and the Hab module into an initial 22 x 970 nautical mile (40.7 x 1,806 km) orbit.

Following this initial orbit insertion, the nominal mission timeline would call for the EUS to perform an ascent burn to circularize the Orion and Hab module into an 100 nmi (115 miles; 185 km).

The EUS will then fire its engines again for the Trans-Lunar Injection burn, which will send Orion, the EUS, and the Hab module into a transfer orbit to the Moon.

Once safely en route to the Moon, Orion will separate from the top of the remaining SLS stack and will likely turn around to mate to the Hab module.

The exact details of this are not yet known as the design process for the DSG continues.

Regardless, over the course of the 3-10 day outward trip from Earth to the Moon, Orion’s auxiliary engines will perform at least four Outbound Trajectory Correction (OTC) maneuvers to refine the craft’s approach to the Moon.

These OTCs will allow Orion/Hab to target a precise point to enter a NRHO around the Moon while the EUS performs a disposal into a heliocentric orbit.

Once Orion and the Hab module have slipped into a NRHO, Orion will maneuver the Hab toward the PPE, and the four-person crew will then connect the two DSG elements together – a moment that will begin in-space construction of the DSG.

Once the Hab module and PPE are successfully mated together, Orion’s crew will perform a series of initial checkout operations over Orion’s 10-20 day stay in NHRO.

After this, Orion will undock from the Hab element and baby DSG, and the journey back to Earth will begin.

As with the outbound trip, the inbound journey will last between 3-10 days, with Orion’s auxiliary engines performing several Return Trajectory Corrections (RTCs) to properly align the craft for a precise point in Earth’s atmosphere for reentry.

According to graphics on the preliminary mission plan, EM-3 will target a splashdown in the Pacific Ocean off the coast of Baja California, Mexico – after which Orion will be loaded onto a recovery ship and brought back to the United States via the Port of San Diego.

Source: Nasaspaceflight.com

 

[Andy44]

Sounds really cool, reminds me of what I was thinking when I built my LOrbS add-on. That's a lot of time for a crew to be beyond LEO. What's the plan to deal with solar flares?

 

[Thunder Chicken]

It takes 2-4 days for a CME to travel from the sun to the Earth, about the same time it would take to get a crew to TEI and get into our magnetosphere. Mission abort seems like a likely alternative unless there is a provision for a storm shelter of some sort.

 

[Andy44]

The article says the inbound journey would take "3-10 days". 3 sounds right by Apollo standards. What could possibly take them ten days to get back? Some sort of exotic propellant-saving trajectory? Taking it a step further, if you need extra time due to propellant constraints, how do you budget for a quick abort when a solar flare is detected?

 

[boogabooga]

The article says the inbound journey would take "3-10 days". 3 sounds right by Apollo standards. What could possibly take them ten days to get back? Some sort of exotic propellant-saving trajectory? Taking it a step further, if you need extra time due to propellant constraints, how do you budget for a quick abort when a solar flare is detected?

A few days in LEO? :shrug:

But difference between Hohmann transfer to moon and escape velocity isn't all that much. And GRAIL-esque low energy trips via Lagrange points take ~30 days, IIRC.

 

[Andy44]

That's an interesting idea...aerobrake into LEO and wait until the orbit passes over the desired splashdown point? In that case they'd under the protection of the magnetosphere, anyway.

 

[BrianJ]

Interesting. I never heard of "Near Rectilinear Halo Orbit" before.
More infos about NRHOs:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019648.pdf

 

[gattispilot]

Sounds like we need to make it happen in Orbiter

 

[Urwumpe]

Interesting. I never heard of "Near Rectilinear Halo Orbit" before.
More infos about NRHOs:
https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019648.pdf

Near Rectilinear Halo Orbit Explained and Visualized - YouTube

This PDF also explains the travel times well - depending on where in the NRO the station is, it can take a short while before the Orion could leave the NRO and travel back home (Without using more fuel for a more rapid abort). Really interesting reading. :thumbup:

 

[gattispilot]

So we can do this:

 

[boogabooga]

Seems to me that "Near Rectilinear Halo Orbit" is a just a highly eccentric lunar polar orbit with perturbations at apoapsis.

 

[francisdrake]

I tried to reach a Near Rectilinear Halo Orbit with the Orion in Orbiter, and this was pretty steep. From literature I chose a 200 x 75000 km polar orbit, with the periapsis over the south pole. The challenge is, that the orbital plane must be perpendicular to the line Earth-Moon, otherwise Earth's gravity deforms the orbit too much over time.

The problem was, when coming directly from Earth, capturing over the lunar south pole, my orbital plane was more or less in-line with Earth-Moon. So I decided to wait until apoapsis (75000 km out) to change planes by 90°, because speed is low out there and plane change maneuvers are cheap (small dV). But Orbiter does not support well far-away maneuvers. The orbital reference changes to Sun, when overriding this manually you cannot use the Autopilots, so the Orbit-normal indicator runs away pretty quick during the burn. In fact I had to cheat myself into this orbit, by scenario-file refuelling.

For a better approach it is probably necessary to aim the TLI burn in front of the Moon and let the moon catch up with you. This way the capturing orbit should roughly be perpendicular to the line Earth-Moon, making the orbital alignment easier.