OrbitalHub

Credits: ESA MPS for OSIRIS Team MPS/UPM/
LAM/IAA/RSSD/INTA/UPM/DASP/IDA

On September 6th, 2008, the ESA’s space probe Rosetta performed the first highlight on its 11 year mission: a close flyby the asteroid 2867 Steins. There are two more important events to occur during the mission, which are another flyby the asteroid 21 Lutetia in 2010 and the actual rendezvous with the comet 67/P Churyumov-Gerasimenko in 2014.

The Rosetta mission is special in many ways. It is the first mission to deploy a lander to the surface of a comet. It will also be the first to orbit the nucleus of a comet and to fly alongside a comet as it heads towards the inner Solar System.

Credits: ESA

Rosetta’s mission began on March 2nd, 2004, when the spacecraft lifted off from Kourou, French Guiana. In order to optimize the use of fuel, the probe has a very complicated trajectory to reach its final target, the comet 67/P Churyumov-Gerasimenko. The long trajectory includes three Earth-gravity assists (2004, 2007, and 2009) and one at Mars (2007). The probe uses the gravity wells of Earth and Mars to accelerate to the speed needed for the rendezvous with the comet. Most of the time, the probe is hibernating with the majority of its systems shut down in order to optimize the power consumption. At the time of the rendezvous, the remaining fuel will be used to slow down the probe to match the speed of the comet.

Credits: ESA/AOES Medialab

After reaching the comet, Rosetta will deploy a lander, called Philae, to the surface. While the probe will study the comet’s nucleus from a close orbit, the lander will take measurements from the comet’s surface. Because the gravity of the comet is very weak, the lander will use a harpoon to anchor itself to the surface.

Rosetta will stay with the comet more than one year, and during this time it will study one of the most primitive materials in the solar system. Scientists hope to discover the secrets of the physical and chemical processes that marked the beginning of the solar system some 5 billion years ago.

Credits: ESA/AOES Medialab

Traditionally, probes sent beyond the main asteroid belt employ radioisotope thermal generators (RTGs) as power generators. RTGs convert the heat from a radioactive source into electricity using an array of thermocouples. Instead, Rosetta is using solar cells for power generation. The probe deploys two impressive solar panels (a total area of 64 square meters). Even when close to the comet, the panels will be able to generate around 400 Watts of power. The panels can be rotated through +/- 180 degrees to track the Sun in every attitude assumed by the probe.

The probe is cube-shaped and measures 2.8×2.1×2.0 meters. At launch, it weighs 3,000 kg, including 1,670 kg of fuel, 165 kg of scientific payload for the orbiter, and 100 kg for the lander. The scientific instruments are accommodated on the lower side of the probe, which will be directed towards the comet during the last phase of the mission. Meanwhile, the probe will orbit the nucleus of the comet. A communication antenna 2.2 meters in diameter will be mounted on one side of the probe and on the opposite side the lander is attached. The other two lateral sides are used for anchoring the solar panels.

Credits: ESA/AOES Medialab

I was able to dig up more information about the probe and the lander in the mission launch kit on the EADS Astrium website.

The prime contractor for the spacecraft is Astrium Germany. The main sub-contractors are Astrium UK, Astrium France, and Alenia Spazio.

For propulsion and attitude control, the probe is using 24x10N bipropellant jets. The propulsion system is at the centre of the probe, where the tanks of propellant are located in the centre of a vertical tube.

I could not find an explanation as to why this design was chosen. Since the ability of the spacecraft to maneuver by using the onboard propulsion system is critical, I am assuming that the fuel tanks have to be protected from possible hits by micro meteorites.

Credits: ESA/AOES Medialab

The scientific instruments onboard Rosetta are: OSIRIS (Optical Spectroscopic and Infrared Remote Imaging System), ALICE (Ultraviolet Imaging Spectrometer), VIRTIS (Visible and Infrared Thermal Imaging System), MIRO (Microwave Instrument for Rosetta Orbiter), ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis), COSIMA (Cometary Secondary Ion Mass Analyser), MIDAS (Micro-Imaging Dust Analysis System), CONSERT (Comet Nucleus Sounding Experiment by Radiowave Transmission), GIADA (Grain Impact Analyser and Dust Accumulator), RPC (Rosetta Plasma Consortium), and RSI (Radio Science Investigation).

The lander is provided by a European consortium lead by the DLR (German Aeronautic Research Institute). Members of this consortium include ESA and the Austrian, Finnish, French, Hungarian, Irish, Italian, and British institutes.

Credits: ESA/AOES Medialab

The lander has a polygonal carbon fibre sandwich structure which is covered in solar cells. The antenna transmits data from the lander via the probe orbiting the comet.

There is an impressive collection of scientific instruments mounted on the lander as well: COSAC (Cometary Sampling and Composition experiment), MODULUS PTOMELY (Gas analyser), MUPUS (Multi-Purpose Sensors for Surface and Subsurface Science), ROMAP (Rosetta Lander Magnetometer and Plasma Monitor), SESAME (Surface Electrical Seismic and Acoustic Monitoring Experiments), APXS (Alpha X-ray Spectrometer), CONSERT (Comet Nucleus Sounding Experiment by Microwave Transmission), CIVA (Imager system using panoramic cameras), ROLIS (Rosetta Lander Imaging System used during the descend phase), and SD2 (Sample and Distribution Device, a sample acquisition system).

Credits: ESA

The scientific data collected by the instruments is transmitted to the Rosetta Mission Operations Centre (MOC) through a 8bps link. Due to the narrow bandwidth, the data cannot be sent back to Earth in real-time and has to be stored on the probe before being relayed.

The MOC at the European Space Operations Centre (ESOC) in Darmstadt has been controlling this long term mission since launch using ESA’s DSA 1 deep-space ground station at New Norcia.

It may seem like a long journey, but as in The Days of the Comet, the Rosetta mission could open up a whole new world of possibilities.

When I read The Fountains of Paradise a few years ago, I thought the space elevator was an interesting concept but that there was little chance of seeing it materialize like we saw the geostationary satellites become a reality after being depicted in a science fiction story by the same author, Arthur C. Clarke. And not just because some famous scientist said so, but because anchoring to the Earth a geostationary satellite with a cable measuring some 100,000 km is quite a technological challenge.

The first scientist to propose building a structure to reach space was Konstantin Tsiolkovski, who envisioned an orbital tower in 1895. In 1960, another Russian scientist, Yuri Artsutanov, developed this concept into an article called Into Space with the Help of an Electric Locomotive, which was published in Komsomolskaya Pravda. Artsutanov proposed linking of geosynchronous satellites to the ground using cables. It is interesting to mention here that Arthur C. Clarke and Yuri Artsutanov actually met years after the Fountains of Paradise was published.

Ok, so it is just science fiction, you might say. Well, not quite. There was a study ordered by NASA under the NASA Institute for Advanced Concepts (NIAC) program, which had as its object the investigation of all aspects of the construction and operation of a space elevator. The study was funded by NASA for more than two years and it was titled The Space Elevator.

A book was also published by the authors of the study, Bradley C. Edwards and Eric A. Westling. The book has the same title as the study. I found the book easy to read and really entertaining. Even if it becomes very technical in some parts, it is accessible to readers who do not have a technical background.

The book starts by presenting the main components of the design (the ribbon, the spacecraft, the climber, and the anchor), and the challenges that the space and the Earth’s atmosphere pose to the space elevator during the deployment phase and during the normal life of the program: lightings, meteors, and LEO objects, just to mention a few.

Being a feasibility study, the economic considerations had to be part of it. There are budget estimates that would draw the attention of potential investors, and even a realistic schedule for the development of not just one, but up to four ribbons.

While the space elevator is obviously a very cheap solution for deploying payloads in Earth’s orbit, it can also be used for opening Mars to human exploration and colonization. An Earth space elevator uploading materials in orbit working together with a space elevator downloading them on Mars would make possible the continuous flow of materials and colonists.

The later chapters of the book present the possible implications of the space elevator on the development of space travel and on the future of our technological society.

As the authors acknowledge, the book is not an exhaustive study of all aspects to be considered in the designing and building of the space elevator, but a good beginning. The proposed budget of 6 to 10 billion dollars for the project is not excessive considering the potential return of investment and that access to space is essential for the future development of our society.

Published in 2003, the book is a classic. I strongly recommend it.

In a follow up to The Space Elevator, Bradley C. Edwards and Philip Ragan wrote Leaving the Planet by Space Elevator, which was published in 2006.

For more information about the space elevator, including the 2008 Space Elevator Challenge and the Elevator: 2010 challenge, check out The Spaceward Foundation’s site.

Credits: NASA

Constellation Program is NASA’s new generation space transportation system. It is designed to cover a wide range of space missions, such as delivering supplies and human crews to the International Space Station (ISS) and traveling beyond low Earth orbit (LEO). The goal of the program is to establish a permanent human presence on the Moon and then go to Mars and other destinations.

The Constellation Program promotes exploration, science, commerce, and the United States’ presence in space.

Constellation consists of two launching vehicles (Ares I and Ares V), the Orion spacecraft, the Earth Departure Stage, and the Altair, which is the Lunar Surface Access Module.

Credits: NASA

Ares I is the crew launch vehicle that will be used to deliver the Orion spacecraft to LEO. Ares I is a two stage rocket, 94 m long and 5.5 m in diameter that can deliver a 25,000 kg payload to LEO.

The first stage is a solid rocket booster that evolved from the Space Shuttle Solid Rocket Booster (SRB). An additional fifth segment was added to the initial SRB design, which enables the rocket to produce more thrust and burn longer. The second stage uses liquid oxygen and liquid hydrogen as fuel. The J-2X engine used by the second stage evolved from the J-2 engine used on the Saturn V rocket.

In addition to its primary mission, Ares I can also be used to deliver resources and supplies to the ISS or to park payloads in orbit for retrieval by other spacecraft bound for the Moon or other destinations.

Credits: NASA

Ares V is the cargo launch vehicle of the Constellation Program. Ares V is a two stage rocket, 116 m long and 10 m in diameter. It will be able to deliver a staggering 188,000 kg (188 metric tonnes!) payload into a LEO.

The first stage uses both solid and liquid propulsion (two SRB-derived boosters and 6 RS-68 liquid fueled engines) while the second stage (the Earth Departure Stage) uses a single J-2X engine. It is a versatile launch system and it will be used to carry to LEO cargo and the components needed to go to the Moon and later to Mars.

Both launch vehicles are subject to configuration changes. The images reflect the configuration as of September 2006.

Credits: NASA

Orion is able to carry four to six astronauts. It will provide logistic support to ISS in the first stage. After that, Orion will become an important part of NASA’s human missions to the Moon and Mars.

The conceptual design is similar to the Apollo, but has been improved: an updated digital control system, automated pilot for docking procedures, and a nitrogen/oxygen mixed atmosphere.

The conical form is the safest and most reliable design for re-entering the Earth’s atmosphere. The landing procedure has also been modified: instead of a splash in the Ocean, the module will land on solid ground using a combination of parachutes and airbags.

Credits: NASA

Altair is the lander spacecraft component of the Constellation Program. Like its predecessor, the Apollo Lunar Module, Altair has two stages.

Altair will land all crew members of the lunar mission on the surface of the Moon, while Orion will stay in lunar orbit until the mission ends. The ascending stage brings the crew back on Orion for the journey home.