[27.09.2018]

The German-French satellite MERLIN (Methane Remote Sensing LIDAR Mission) is a mission to observe the concentration of the greenhouse gas methane. In this cooperation between CNES and DLR, CNES signs responsible for the Satellite Bus, which is a Myriade Evolution, and DLR signs responsible for the Instrument. The instrument on MERLIN is a pulsed high power LIDAR (Light Detecting and Ranging) operating precisely at the methane absorption lines at 1645.55 nm wavelength. The instrument emits two different wavelengths called ‘online’ and ‘offline’: Online means located in the absorption feature and offline beside it for reference purposes.

To enable the required emission wavelengths around 1645.5-1645.7 nm, a frequency reference unit (FRU) is part of the instrument on the satellite. The frequency reference unit contains a methane gas cell, several diode lasers (1064 nm and 1645 nm emission wavelength), a wavemeter and the associated control electronics including an FPGA for stabilizing the diode laser emissions and the high power laser pulse frequency to the methane cell and the wavemeter. The FRU is delivering its optical signals to the high power laser and measures their wavelengths and the ones of the high power laser pulses to MHz accuracy. In addition it performs the wavelength stabilisation control loops for the internal diode laser and of the OPO of the high power laser.  

One and a half years after the start phase C/D, SpaceTech GmbH delivered the CDR data package for the frequency reference unit to Airbus and DLR. The co-location took place on the 25th and 26th of July 2018 at the SpaceTech premises in Immenstaad. All RIDs have been closed and no showstoppers for the CDR have been found. The engineering model has been built and  its final testing phase has started.

After the successful operation of the LRI on GRACE-FO in orbit, the development of the frequency reference unit is the next major C/D development activity for a laser-optical instrument at SpaceTech.

Key and driving requirements of the FRU are:

• 5 mW of optical output power at 1645 nm with a laser frequency accuracy and stability of  10 MHz
• 10 mW of optical output power at 1064 nm with less than 1 MHz linewidth
• Measurement of every single transmitted pulse with a systematic error of less than 8 MHz
• Controlling the cavity of the optical parametric oscillator in the main laser

Links:
DLR Site in MERLIN (http://www.dlr.de/rd/desktopdefault.aspx/tabid-2440/3586_read-31672/)
Animated in orbit maneuvers of the MERLIN satellite: https://www.youtube.com/watch?v=tmlSAB-ltek
Scientific publication: http://www.mdpi.com/2072-4292/9/10/1052

		MERLIN Satellite [CNES]
		Transparent model view of the FRU
		Picture of the engineering model of the FRU

Das diesem Bericht zugrundeliegende FE-Vorhaben wird im Auftrag des Bundesministeriums für Wirtschaft und Energie (BMWi) unter dem Förderkennzeichen 50EP1301 durchgeführt. Die Arbeiten sind Teil einer Kooperation zwischen DLR Raumfahrt-Management und CNES beim deutsch-französischen MERLIN-Satellitenprojekt. STI führt die Arbeiten im Unterauftrag der Firma Airbus DS GmbH, Ottobrunn durch. Die Verantwortung für den Inhalt dieser Veröffentlichung liegt beim Autor.

[15.08.2018]

Today, starting 18:00 CEST/German time, the ICARUS antenna will be installed outside the service Module Zvezda by the russian Cosmonauts Oleg Artemyev and Sergey Prokopyev. The Extra-Vehicular Activity wll be coverd live by NASA TV under:

https://www.nasa.gov/multimedia/nasatv/index.html#public (starting 17:00 CEST/German time)

With 5-7 hours, this is one of the longest EVAs ever performed by russia. After the final system level tests, the payload is planned to be fully operational at the beginning of Autumn.

ICARUS payload is designed to receive science information from miniaturized devices attached to animals, known as tags, and send reconfiguration commands if needed. The hardware on the ISS is designed to communicate with more than 100 tags simultaneously, providing the capability of daily communication with thousands of devices around the Globe.

SpaceTech GmbH has developed, manufactured and tested the ICARUS payload over the last 4 years as leader of a team of German SMEs. The project was commissioned by the Max Planck Institute for Ornithology and is funded by the German Space Agency DLR in cooperation with Roscosmos.

[04.07.2018]

We are proud to announce that with the activation of the Laser ranging interferometer (LRI) on GRACE Follow-On on June 13th 2018, the first optical instrument flight hardware of SpaceTech is fully operational in orbit! This is a major milestone for our activities in the field of laser-optical intrumentation and proof of STIs capabilities to provide top notch optical instrument equipment.

The LRI measures the changes of the inter-satellite distance of the two GRACE FO satellites flying in approx. 220 km distance to each with unprecedented accuracy down to several ten nanometers (about 1/1000th of the thickness of a human hair).

Under contract to the Geoforschungszentrum Potsdam (GFZ) (and under the scientific lead of Albert Einstein Institute Hannover - AEI) SpaceTech signed responsible for the development of the optical bench, the retroflector, and the instrument baffles of the LRI, starting from prototypes to EM, QM and FMs for both satellites. On the German side, the photoreceivers of the optical bench were provided by DLR Institute for optical systems in Berlin, while STI subcontracted Airbus DS and Hensoldt Optronics for the steering mirror on the optical bench and the manufacturing and assembly of the Zerodur parts of the retroreflector . On the US side we had a close cooperation with JPL who where responsible for the mission and provided the US part of the LRI (the laser, the cavity & the phasemeter).

The optical bench (shown above), consisting of an titanium optical bench with integrated and attached high performance laser optics, receives the laser signal via an optical fiber interface, launches the beam out of the fiber into free space, shapes it and directs it to µrad accuracy to the second spacecraft by means of a fine steering mirror. In addition it receives the laser signal from the second spacecraft and superimposes it with the local signal onto quadrant photoreceivers to aqcuire the DWS and heterodynes signal for the ranging measurement.  Main challenges in the development were the high wavefront planarity requirement of lambda/12 (pv), the beam alignment error of less than 10 µrad and the ranging noise contribution of less than 5 nm/sqrt(Hz). To achieve this a low thermal noise, low mechanical stress, highly stable optical bench design was developed, including a newly designed ultra-stable monolithic beam collimator, which is now available for further applications.

The retroreflector (shown above) , consisting of an ultra-stable carbon-fiber structure with attached zerodur optics, routes the laser beam around the center of mass of the respective spacecraft, essential to achieve Nanometer accuracy to the ranging measurement. Main challenges of this development were the limited available space in the satellite in conjuction with the demanding mirror alignment error of less than 40 µrad, less than 400 nm/K vertex stability and less than lambda/15 wavefront planarity(pv). 

A first evaluation of the measurement of the laser ranging interferometer is shown in the picture below

graphic: B. Knispel/G.Heinzel/Max Planck Institute for Gravitational Physics; GRACE FO data: NASA, GFZ, JPL; map data: SRTM

In addition the the contribution to the LRI equipment, STI has been  responsible for:

• the LRI instrument integration @ STI facitlities in cooperation with JPL, DLR Bremen, Airbus DS and AEI
• the spacecraft primary structures (structural analysis and procurement)
• the ASTSS tertiary structure (manufactured by CST)
• the deployable S-Band boom
• the Coarse Earth-Sun-Sensors (CESS)
• the satellite MGSE & transport containers

We did this in contract to the Geoforschungszentrum Potsdam (GFZ) for the LRI  (and under the scientific lead of Albert Einstein Institute Hannover - AEI) and in subcontract to Airbus DS for the other contributions and in close cooperation with our collegues at JPL, the DLR Institutes in Bremen and Berlin Adlershof as well as Hensoldt Optronics.

STI is proud to be part of this mission and thankful for the great cooperation of all project partners!

Much more information on GRACE Follow-On can be found here:

• https://gracefo.jpl.nasa.gov
• http://www.aei.mpg.de/2277280/first-light-for-grace-follow-on-laser-interferometer
• https://www.gfz-potsdam.de/sektion/globales-geomonitoring-und-schwerefeld/projekte/gravity-recovery-and-climate-experiment-follow-on-grace-fo-mission/

[22.5.2018]

Left; Launch [Credit: NASA/Bill Ingalls] ; Right:Artists Impression of GRACE Follow-On [Credit:NASA]

6 years after project start (and many more after first discussions on the successor to the GRACE mission), the US-German Gravity mission GRACE Follow-On has successfuly launched yesterday 12:49 PST, in perfect weather with a beautiful blue sky, the two Grace Follow-On Satellites launched onboard of a Falcon 9, together with 5 Iridium Satellites.

Everything is looking good. There have be no issue before or during the launch, the satellites deployed as planned and telemetry shows both satellites are healthy. The instruments will be put into operation over the next weeks.

GRACE Follow-On will continue the GRACE success story and flies the first inter-satellite laser interferometer, which may also be seen as a LISA technology pathfinder. For STI, being responsible for the German contribution to the laser ranging interferometer, this is the first laser-optical equipment in space, along with other equipment provided by us.

A video of the launch can be found here: https://www.youtube.com/watch?v=y3niFzo5VLI

STI workshare

STI has significantly contributed to GRACE Follow-On, namely we where responsible for:

• the Gerrman contribution of the laser ranging interferometer (the optical bench, the retroreflector and the instrument baffles)
• the LRI instrument integration @ STI facitlities in cooperation with JPL, DLR, Airbus DS and AEI
• the spacecraft primary structures (structural analysis and procurement)
• the ASTSS tertiary structure (manufactured by CST)
• the deployable S-Band boom
• the Coarse Earth-Sun-Sensors (CESS)
• the satellite MGSE & transport containers

We did this in contract to the Geoforschungszentrum Potsdam (GFZ) for the LRI  (and under the scientific lead of Albert Einstein Institute Hannover - AEI) and in subcontract to Airbus DS for the other contributions. On the US side we had a close cooperation with JPL who where responsible for the mission and provided the US part of the LRI (the laser, the cavity & the phasemeter).

STI is proud to be part of this mission and thankful for the great cooperation of all project partners!

Much more information on GRACE Follow-On can be found here:

• http://spacetech-i.com/products/optical-instruments/grace-fo-laser-ranging-interferometer
• https://gracefo.jpl.nasa.gov
• https://www.gfz-potsdam.de/sektion/globales-geomonitoring-und-schwerefeld/projekte/gravity-recovery-and-climate-experiment-follow-on-grace-fo-mission/
• https://www.aei.mpg.de/179419/04_Grace_Follow-on