JWST – The James Webb Space Telescope

by Dave Fischer

James Webb Space Telescope
James Webb Space Telescope – Deployed
Credit: NASA Video

The James Webb Space Telescope (JWST) is an infrared observatory, and a partial successor to the Hubble Space Telescope. JWST does not view visible light because light from the earliest universe has shifted toward the infrared (red shift).

Infrared sensitivity is required in order to see further back in time toward the beginning of the universe than either Hubble or ground based observatories.The James Webb Space Telescope is a joint venture between NASA, the European Space Agency (ESA) and the Canadian Space Agency (CSA). In all, fifteen countries are making contributions to JWST.

The are four main components to the scientific mission:

  • Search for the first stars and galaxies that formed after the Big Bang
  • Study galaxies and their formation and evolution
  • Understand the formation of stars and planetary systems
  • Study the origins of life on planetary systems

JWST is scheduled for launch in 2014 aboard an Ariane 5 rocket. It will take up residence at the Sun-Earth Lagrange point 2 (SEL-2). SEL-2 is 1,500,000 km beyond the Earth from the Sun (the Earth-Moon L2 is only 61,500 km beyond the Moon). The location was chosen in order to be able to shield the telescope from the infrared radiation of the Sun and the Earth.

Currently, SEL-2 is occupied by the Wilkinson Microwave Anisotropy Probe (WMAP), which was launched 30 June 2001, and the Herschel and Planck observatories, which were launched together on an Ariane 5 on 14 May 2009.

The image at left is a cutaway diagram the the Ariane 5 rocket, illustrating how the JWST will fold up inside the payload fairing. With the large screen behind it, the JWST will be about 21 m in width. It will stand about three stories high. The main telescope mirror, which measures 6.5 m in diameter, is too large to launch in one piece. Instead, it consists of 17 individual mirror segments mounted on a frame which will be folded inside the fairing of the Ariane 5 at launch.

Once it arrives at SEL-2, it will unfold, as this animation shows.

There are four instruments in the Integrated Science Instrument Module designed to conduct the investigations on board the James Webb Space Telescope:

Cutaway: JWST inside Ariane 5
Image Credit: European Space Agency

Four Instruments
Image Credit: NASA

  • Mid-Infrared Instrument, or MIRI – provided by the European Consortium with the European Space Agency (ESA), and by the NASA Jet Propulsion Laboratory (JPL)
  • Near-Infrared Camera, or NIRCam – provided by the University of Arizona
  • Near-Infrared Spectrograph, or NIRSpec – provided by ESA, with components provided by NASA/GSFC.
  • Fine Guidance Sensor, or FGS – provided by the Canadian Space Agency. The FGS contains a dedicated Guider and a Tunable Filter Camera.

The image below shows the locations of the four instruments in the Integrated Science Instrument Module (ISIM). Below, the image shows the location of the instrument package within the JWST.

Image Credit: NASA

The Mid-Infrared Instrument (MIRI) is an imager/spectrograph that covers the wavelength range of 5 to 27 micrometers. The camera provides wide-field broadband imagery, and the spectrograph module provides medium-resolution spectroscopy over a smaller field of view compared to the imager. The nominal operating temperature for the MIRI is 7K. Additional information can be found at the MIRI website, Space Telescope Science Institute.

The Near Infrared Camera (NIRCam) is an imager with a large field of view and high angular resolution. The NIRCam covers a wavelength range of 0.6 to 5 micrometers. More on NIRCam.

The Near Infrared Spectrograph (NIRSpec) measures the simultaneous spectra of more than 100 objects in a 9-square-arcminute field of view. This instrument provides medium-resolution spectroscopy over a wavelength range of 1 to 5 micrometers and lower-resolution spectroscopy from 0.6 to 5 micrometers. See the Space Telescope Science Institute information on NIRSpec.

The Fine Guidance Sensor (FGS) sensor is used for both “guide star” acquisition and fine pointing. See information from the Space Telescope Science Institute about NIRSpec.

See also:

The Wikipedia article on JWST.
NASA home page for JWST.
ESA home page for JWST.
CSA home page for JWST.
Make your own Paper Model of the JWST.
YouTube and JWST.

Let us know what you think. What do you want to know about? Post a comment.

Desert RATS

by Dave Fischer

If you want humanity to explore the Solar System, you have to test the systems you plan to use for moving around and living. And where is there a readily available harsh environment for such testing? Arizona. In the Summer it is hot and dry. In the Winter it is cold and dry (or wet, depending on the state of the Arctic storm systems).

Currently underway (31 August through 15 September) is the 13th iteration of the Desert RATS program. You can follow their exploits on the RATS’ Blog.

RATS site in Northern Arizona
Image Credit: NASA

NASA Athlete Vehicle
(All-Terrain Hex-Legged
Extra-Terrestrial Explorer)
Image Credit: NASA

Space Exploration Vehicle
Image Credit: NASA / Regan Geeseman

NASA’s Research and Technology Studies (RATS) program is designed to gather engineers, astronauts and scientists and test technology. This year, the major objectives include:

  • Space Exploration Vehicles (pdf) – a pair of rovers that astronauts will live in for 7 days at a time
  • Habitat Demonstration Unit (interactive pdf)/Pressurized Excursion Module – a simulated habitat where the rovers can dock to allow the crew room to perform experiments or deal with medical issues
  • Tri-ATHLETEs, or –Terrain Hex-Legged Extra-Terrestrial Explorer – two heavy-lift rover platforms that allow the habitat, or other large items, to go where the action is
  • Portable communications terminals
  • Centaur 2 – a possible four-wheeled transportation method for NASA Robonaut 2
  • Portable Utility Pallets, or PUPs for short – mobile charging stations for equipment
  • A suite of new geology sample collection tools, including a self-contained GeoLab glove box (pdf) for conducting in-field analysis of various collected rock samples.

During this mission, there will be four crew members living in the two rovers. Their traverse routes will include driving up and down steep slopes and over rough terrain at various speeds. The crew will also demonstrate docking and undocking with the PUPs and the habitat. Other objectives for the rovers include demonstrating the differences in productivity for crew members and their ground support that come with different communication methods, and evaluating different operational concepts for the trips the rovers make.

Let us know what you think. What do you want to know about? Post a comment.


by Dave Fischer

Commercial Reusable Suborbital Research Program

NASA has awarded $475,000 as part of its program to development recoverable launch vehicles to be used for small payloads going to “near-space,” the region of Earth’s atmosphere between 65,000 and 350,000 feet. The awards were made under the CRuSR program (Commercial Reusable Suborbital Research Program). NASA’s press release states:

The CRuSR program fosters the development of commercial reusable transportation to near space. The overall goal of the program is regular, frequent and predictable access to near-space at a reasonable cost with easy recovery of intact payloads.

The awards were made to Armadillo Aerospace, home to the Super-Mod vehicle, and Masten Space Systems, home to the Xaero vehicle.

Armadillo will fly three missions from Spaceport America in New Mexico. Two are schedule for an altitude of nine miles each, and the third is scheduled for 25 miles (132,000 feet – 40,200 meters).

Masten will fly four missions this winter from the Mojave Spaceport in California. Two of the flights are slated for three miles and two are slated for 18 miles (95,000 feet – 29,000 meters).

Image Credit: Armadillo Aerospace
Image Credit: Masten Space Systems

Let us know what you think. What do you want to know about? Post a comment.

Pintle Injector Rocket Engines

by Dave Fischer

We have had several queries concerning “pintle injectors” (make sure you read the last paragraph of this post), as these are mentioned in the Space-X page on the Falcon 9, where it refers to the Merlin rocket engine and the “pintle style injector“:

The main engine, called Merlin 1C, was developed internally at Space-X, drawing upon a long heritage of space proven engines. The pintle style injector at the heart of Merlin 1C was first used in the Apollo Moon program for the Lunar Excursion Module (LEM) landing engine, one of the most critical phases of the mission.

Based on the queries and the Space-X information, we went sleuthing. First, we came across the fact that TRW built the LEM descent engine, which used the pintle injector. We ran across David Meerman Scott’s blog apolloartifacts for a discussion and look at a model of the famous Lunar Module Descent Engine (LMDE). The engine was made famous by the Apollo 13 mission, where:

the Service Propulsion System (SPS) was never used subsequent to the cryotank stir/explosion. Because the extent of damage to the SPS was unknown, there was great concern at the time that collateral damage could have caused a catastrophic malfunction (if the engine was fired). Instead the LMDE was used for the return burn and subsequent course correction. Quite a famous engine.

In 2000, TRW demonstrated the TR-106 engine (pintle injector) using LOX / LH2 at NASA’s John C. Stennis Space Center . The engine generated 650,000 pounds of thrust, more than the 400,000 pounds of thrust generated by the Space Shuttle Main Engine SSME. Al Frew, vice president and general manager, TRW Space & Technology Division stated:

Most engines are designed for maximum performance and minimum weight, but we deliberately set out to develop an engine that minimizes cost while retaining excellent performance. We believe this engine will cost 50 to 75 percent less than comparable liquid hydrogen boosters. By reducing engine costs, which make up almost half of the cost of a launch vehicle, we will reduce the cost of launch vehicles and access to space for government and commercial customers.

Despite the promise the motor demonstrated, NASA canceled further work.

The pintle injector engines have a long history in the former Soviet Union. The NK-33 was the successor to the NK-15 engines used in the failed Soviet N1 Moon launcher. NK-33 have been used with the Russian Proton launch system. An interesting discussion of the Soviet Moon rocket, its engines and the NK-33 successor can be found here, along with spectacular video of the launch and explosion. Orbital Sciences has now contracted with Aerojet (owner of the NK-33 engines) to finish developing and testing the NK-33 engines, now designated as AJ26-58 for the Taurus II.

Jonathon Goff, at Masten Space Systems, had a commentary at Selenianboondocks on the 2006 Space-X change from an ablative Merlin engine to a regenerative engine. Jon states that the “engine related problems are interrelated, and that they have to do with the combination of using a high chamber pressure engine design with a pintle-injector and an ablatively cooled chamber wall.” That is, the flame produced by the cone of fuel and oxidizer hits the wall of the chamber and overheats the wall.

Included in the commentary is a simplified image of a pintle injector rocket engine, which illustrates the flow of liquid oxygen and fuel (RP-1 or liquid hydrogen) through the pintle injector into a cone shaped spray in the combustion chamber.

The replacement of the ablative chamber with a regenerative chamber eliminates the overheating.

Pintle Injector
Pintle Injector
Image Credit: Forschungsgruppe Alternative Raumfahrtkonzepte

Below left is the business end of the LEM Descent engine, showing the Pintle Injector:

Below right is an image by Warren W. Thompson at the unveiling of Space-X’s Falcon 1 at the Air & Space Museum on 4 December 2003.

Lunar Module Descent Engine
Image Credit: jurvetson on Flickr
Merlin Engine with Pintle Injector
Merlin Engine with Pintle Injector
Image Credit: Warren W. Thompson

Finally, while explaining the Pintle Injector to a friend, I realized that almost everybody who has a garden or tends a lawn has personal experience with pintles. You all use a nozzle on the end of your watering hose. Crank it down and you get a steady, narrow stream of water shooting out in a long arc. Crank it back the other way when you want to shut it off, and you get a wide, cone shaped fan spray. Now, turn off the water and look at the business end of the garden hose nozzle (please shut the water off first). There in the middle is a round pintle that moves back and forth as you crank the outer casing one way or the other. And the fan shaped spray of water with which you are familiar is what the fuel and oxidizer spray looks like inside the rocket engine. So take another look at the two images above and imagine the fan shaped spray. The only difference is that your spray of water doesn’t explosively combust and throw a rocket into space.