Mars flyby mission

Team ΔV

Ilya Belikov,

Alexander Bogdanov,

Nadezhda Paltusova.

Goals and requirements The goal of this study is to minimize the complexity, costs and risks of initial Inspiration Mars flyby-

project [1]. For that purpose, the following aspects were taken into account:

- It is unlikely, that there will be major NASA support and funding of 2018 flyby mission (as it is transferred to 2021) [2]. For this

reason, there is only a weak opportunity to use SLS launch vehicle;

- Atmospheric reentry at a hyperbolic speed poses a high risk. Development and proper testing of the Earth Reentry Pod will

require considerable efforts to build and test it (at hyperbolic speed) in space;

- Lack of living space can negatively affect the psychological state of the crew during the long flight;

So we tried to reduce the influence of these factors. The following changes were made:

- Mission was shifted from the government agency (NASA) to a private company to be able to reduce dependence on public

policy , and focus on solving technical and financial problems;

- Propulsion module was added, to reduce high speed before reentry;

- Habitable volume was increased by more than twice, using inflatable habitat module and larger space capsule (DragonRider).

Launch vehicle

We examined the possibility of using various launch vehicles that is available on the market (mixed

scheme). The option of using SpaceX Falcon Heavy was also considered (proposed scheme).

* because of inclination differences, overall mass to LEO will be less than 112 mT.

As it can be seen, using Falcon Heavy gives an advantage in both price and complexity.

According to SpaceX [3], it is planned to perform qualification flight of Falcon Heavy this year

(2014). So this vehicle has a good chances to be ready to launch in 2017.

Trajectory design We use the trajectory proposed by Inspiration Mars team. However, there is a differences in launch date.

We assume 12/15/2017 launch instead of 1/4/2018. It leads to increased C3 and reduced reentry speed.

As it has been studied, this case is more convenient than opposite (reduced C3 and increased reentry

speed).

Mars Flyby Vehicle

Mars Flyby Vehicle (MFV) includes three modules: inflatable Habitat module, DragonRider capsule and

Service module.

Inflatable habitat module The habitat is based on Bigelow BEAM inflatable

module, which is being prepared to be tested on

ISS.

Additional hardware: NASA Docking System

(NDS) and Navigation and Communication

system, both are in development now for various

NASA projects.

Navigation and communication module includes

low- and high-gain antennas (similar to Orion

MPCV) and star trackers.

It is supposed to perform communication through

NASA Deep Space Network (as it is with Orion

MPCV).

In comparison with standard “aluminum can”

module design (ISS or Cygnus), inflatable design

allows to improve radiation shielding [4] and

decrease mass.

DragonRider

DragonRider spacecraft is now in development by

SpaceX under Commercial Crew Transportation

Capability program. It is supposed to fly on orbit

in the next 2 to 3 year [5]

Nasa Docking System (NDS) is expected to be

mounted on the capsule. The spacecraft will likely

to be able to perform fully automated docking. [6]

We can use Dragon Reaction Control System

(RCS) to provide attitude control for the Mars

Flyby Vehicle.

Due to increased pressurized volume (in

comparison with IM-proposed 2-seat Orion

Reentry Pod), there is more living space for the

crew

DragonRider: ECLSS

Environmental Control and Life Support System is the critical element for this

mission. It was founded by Paragon Space Development Corporation and

Inspiration Mars team, that ECLSS mass is about 6000 kg assuming critical

margins and state of the art technologies.

If we use an advanced technologies then System mass could be reduced for

less then 3000 kg.

In our study we assumed a moderate use of an advanced technologies.

Moreover, it was expected that there is no need to include such systems as air

circulation, temperature and humidity control into ECLSS, because they are

already in the DragonRider ECLSS [7]

So, we assume that ECLSS mass (additional to DragonRider one) can be

lowered to 5000 kg.

Dragon Rider: attitude control

We use DragonRider vehicle, equipped with

its Draco reaction control system (RCS) as

part of the MFV. So there is no need in

additional RSC to perform pitch, yaw, roll or

pitch-over maneuvers.

However, the MFV with fully fueled service

module (at the start of the mission) is

definitely too heavy for DragonRider RCS.

So, to perform translation maneuvers during

orbital rendezvous and docking, we need to

equip it with its own Reaction system.

It’s supposed that additional RCS system will

be mounted on the payload adapter section,

that will connect Falcon Heavy second stage

and propulsion module.

After docking operation is performed, the

payload adapter is detached from the

spacecraft.

Service module

Service module is based on DragonRider Trunk section. It can be

made of two standard 2.9-m Trunks.

To reduce complexity and development cost , we equip it with

hypergolic propellant system.

Hypergolic advantages:

- high boiling point that allows to simplify tanks temperature control

system (it`s not so easy in the case of cryogenic components);

- long-term experience of hypergolics storage in zero gravity.

- better Isp in comparison with solid propellant systems.

- pressure-fed hypergolic engines are far less complicated than pump-

fed cryogenic ones;

One major drawback is a toxicity of such propellant. But in fact we

don't have many options cause Solid or Hybrid propulsion needs in

pressure-resistant propellant tank (with pressure higher than that

required for liquid-fueled pressure-fed engines) that increases overall

system weight.

Service module: engines Here we will compare available hypergolic engines.

The main requirements for choosing an engine are: flight-proven reliability, low mass and dimensions and availability on the

market.

Finally, AJ10-190 engine was selected due to it's incredible design life. The other options such as Russian 14D30, or

European Aestus and RS-72 ware rejected for various reasons, including unproven reliability for RS-72 or unclear availability

for American customers.

And for the Aj10-118K it is expected that it`s design life is too short because of ablative method of chamber cooling.

Spacecraft orbit assembling

1 – 1st Falcon Heavy launchwith inflatable Habitat andECLSS as a payload

2 – 2nd Falcon Heavy launchwith DragonRider and Servicemodule as a payload

3 – Docking andassembling thespacecraft

Orbital maneuvering: docking

Orbital maneuvering To perform the Mars transfer trajectory insertion we use two-burn maneuver.

Initial position is on circular orbit (LEO, 185 km). Then the Falcon Heavy upper stage perform the first

burn to transfer spacecraft on the intermediate elliptic orbit.

When spacecraft reaches perigee of the ellipse, it is time for the second burn, that place spacecraft to the

hyperbolic orbit to Mars. Before the second burn, upper stage is detached from the Mars Flyby Vehicle.

To perform the first burn, Falcon Heavy second stage is used. The Second burn is performed using the

Service module (pitch over maneuver is needed before burn).

Orbital maneuvering: subsystems mass

All burns are considered impulsive

Gravity loses are supposed to be zero.

Orbital maneuvering :

Mars transfer trajectory insertion

Orbital Maneuvering: interplanetary flight

Orbital maneuvering:

Earth orbital insertion

Mission margins There are a kind of simplification in our

calculations: all burns were considered impulsive.

In fact, only for the first burn this can be true. But

the other two burns are not impulsive and therefore,

suffer from gravitational losses.

Though there are some margins in ΔV, they are

probably too low to guarantee that this mission is

able to perform.

Nevertheless, there is one undiscussed question:

whether two-burn maneuver, that we used to escape

from Earth gives an advantage in comparison with

standard direct-burn escape maneuver.

These two maneuvers were analyzed in study [8].

And according to the author, the two-burn escape

maneuver gives an advantage of about 5 to 25 %,

depending on conditions.

So, assuming 5% payload mass margin we can be

more confident in the results of this study.

It is, however to be confirmed later.

Radiation protection

According to the recent research [8], there would be

no fatal danger for the crew from cosmic radiation

during space trip to Mars and back.

It was estimated that excess risk of cancer would be

no more than 3%.

However, the main danger comes from Solar

Energetic Particles (SEP) generated during the Solar

Particle Events. This events are rare, but capable to

even kill the crew.

We proposed a radiation shielding technique to

protect the crew from solar wind particles and

reduce the power of SEP`s flux.

The method is in proper orientation of spacecraft

relative to the Sun. So that, we can use Service

module propellant as a shield against solar particles.

Radiation protection

It is known that liquid propellant, placed in zero

gravity may spread over the walls of the vessel.

Assuming that all tank surface are covered with liquid

layer with constant thickness we can calculate that

areal density of propellant is about (60÷70) g/cm3. for

14.5 mT propellant load (all the way to Mars and

back).

If we take into account propellant mixture ratio for

AJ10-190 (that is about 1.65 NTO/MMH) and

chemical composition of propellant (i.e. mole

fractions of oxygen, hydrogen and nitrogen) than it is

clear that mass fraction of hydrogen is about 8% or

≈ 5 g/cm3

So, even if we do not consider radiation shielding

effect of nitrogen and oxygen, propellant load is

equivalent to 5 g/cm3 of hydrogen or 0.3÷0.4 m thick

layer of water. [10]

Costs and schedule

References:

1) IEEE Aerospace Conference Paper: “Feasibility Analysis for a Manned Mars Free-Return Mission in 2018”, Tito

et all, presented at Big Sky, MT – March 2, 2013

2) Inspiration Mars Sets Sights on Venus/Mars Flyby in 2021., by Dennis Tito, Spacenews.com, 03/03/2014

3) SpaceX launch manifest, http://www.spacex.com/missions

4) Bigelow aerospace official site; BA-330 page, http://www.bigelowaerospace.com/ba330.php

5) SpaceX Dragon page http://www.spacex.com/dragon

6) Unofficial information according to Ken Bowersox http://forum.nasaspaceflight.com/index.php?topic=29182.75

7) Dragon spacecraft datasheet http://www.spaceflight101.com/dragon-spacecraft-information.html

8) Two-burn escape maneuver with an intermediate coasting ellipse, by Edward A. Willis jr., Lewis research center,

Cleveland, Ohio, 1969

9) Curiosity radiation results., by Robert Zubrin, http://www.spacenews.com/article/opinion/35865curiositys-

radiation-results , 06/18/2013

10) Materials for shielding astronauts from the hazards of space radiation, J. W. Wilson et all, NASA centers

collaboration.