NASA Messenger extends its mission life using Helium

Now orbiting the planet Mercury after over ten years in space, NASA's MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft is still functioning better than expected.

Its mission will soon come to an end though, it's running out of fuel and is scheduled to crash into the planet in March.

However, mission control have come up with a novel plan that will use the helium used to pressurize the unmanned probe's engine to give it another month of life.

According to the MESSENGER team, fuel is usually the last problem that a robotic exploration team worry about because there are so many other things that can go wrong long before it runs out.

That being said, the fuel is the single most important consumable aboard an orbiter mission because it not only allows the spacecraft to maintain the correct attitude and keep its antennae pointed at Earth, it also lets it use the main engine to boost its orbit against atmospheric drag, which decays the orbit.

The upshot is that when the propellant runs out, the spacecraft starts to tumble and spirals in to burn up in the atmosphere or, in MESSENGER's case, crash into the surface at hypersonic speed.



So normally when the fuel runs out, that's it, but NASA reasoned that MESSENGER's liquid-fuel rocket engine design meant there was still a bit of thrust left even after all the propellant was expended.

The MESSENGER's engine is pressure fed, which means that it uses helium from a separate tank to push the fuel and oxidizer into the engine's combustion chamber.

Since the helium needs to work against the force of the rocket's combustion, it's under considerable pressure, and when the fuel is gone, there will be some helium left in the pressure tank.

The idea is to use the helium as a cold propellant. In other word's where the rocket engine gets its thrust by burning fuel, the helium pushes the spacecraft by simple gas pressure like a toy balloon when the open neck is let go.

Unfortunately, this is the first time a pressurant has been as an improvised thruster and MESSENGER's engine is a bit more complicated than a balloon.

According to MESSENGER Mission Systems Engineer Dan O’Shaughnessy, of the Johns Hopkins University Applied Physics Laboratory (APL), the pressure in the helium tank isn't much compared to a firing engine.

In addition, the gas passes through a number of reduction valves and nozzles that have to be taken into account, and helium is the second lightest of gases, so it doesn't provide much in the way of thrust.

If these problems can be overcome, NASA estimates that it will give MESSENGER another month of active life before impact on Mercury. MESSENGER's current closest approach to Mercury is 25 km (15 mi).

If a scheduled course correction using the helium is successful, this will rise to 80 km (50 mi). This will allow the orbiter to carry out additional low altitude observations, including collecting a new set of high-resolution images.

"During the additional period of operations, up to four weeks, MESSENGER will measure variations in Mercury’s internal magnetic field at shorter horizontal scales than ever before, scales comparable to the anticipated periapsis altitude between 7 km (4 mi) and 15 km (9 mi) above the planetary surface," says APL’s Haje Korth, the instrument scientist for the spacecraft's magnetometer.

"Combining these observations with those obtained earlier in the mission at slightly higher altitudes will allow the depths of the sources of these variations to be determined. In addition, observations by MESSENGER’s Neutron Spectrometer at the lowest altitudes of the mission will allow water ice deposits to be spatially resolved within individual impact craters at high northern latitudes."

Built and operated by John Hopkins University for NASA, the MESSENGER spacecraft was launched from Cape Canaveral on August 3, 2004 as the first mission aimed to place an orbiter around the innermost planet Mercury. 

Rapid Coordination Extends Space‐Based Sun‐Climate Record

Total solar irradiance (TSI), a measure of how much solar radiative energy hits the entirety of Earth, is the principle energy input to the global climate system.

Collecting accurate TSI data spanning multiple years helps scientists understand how much solar radiation is deposited in the atmosphere and at the surface and thus how much energy is available to influence weather, climate, the cryosphere, atmosphere dynamics, and ocean currents.

Because of TSI’s relevance for natural climate change, TSI has been identified within the US president’s National Plan for Civil Earth Observations [ Holdren, 2014 ] as a vital observation for determining the Earth’s net energy balance.

Similarly, within the National Oceanic and Atmospheric Administration (NOAA) Climate Data Record program, TSI is recognized as an important long‐term measurement for a robust, sustainable, and scientifically defensible approach to climate change
research.

Unfortunately, the main contributors to the TSI record have terminated their observations or are suffering degraded performance.

These include the NASA Active Cavity Radiometer Irradiance Monitor Satellite (ACRIMSat), whose mission ended in December 2013 due to battery problems after nearly 14 years in orbit; the Swiss Precision Monitor Sensor (PREMOS) instrument aboard the French Picard satellite, whose mission ended in March 2014; and the Variability of Solar Irradiance and Gravity Oscillations (VIRGO) aboard the European Space Agency/NASA Solar and Heliospheric Observatory (SOHO), which is still operational, albeit with degraded performance, after 18 years in orbit.

To ensure the longevity of the TSI record without data gaps, scientists had to work fast.

Extraordinary teamwork between NASA, the Laboratory for Atmospheric and Space Physics at the University of Colorado (CU‐LASP), NOAA, and the Air Force over the last few years has enabled the extension of TSI measurements.

This cooperation has included revitalizing the Solar Radiation and Climate Experiment (SORCE, see Image ), an aging NASA satellite launched in 2003; the launch and initial operations of the TSI Calibration Transfer Experiment (TCTE), a NOAA/NASA irradiance instrument aboard an Air Force satellite; and identifying a new opportunity for deployment on the International Space Station (ISS) in 2017 of the NOAA Total and Spectral Solar Irradiance Sensor (TSIS).

Read the full report here

Hubble extends stellar tape measure 10 times farther into space

By applying a technique called spatial scanning to an age-old method for gauging distances called astronomical parallax, scientists now can use NASA’s Hubble Space Telescope to make precision distance measurements 10 times farther into our galaxy than previously possible. 

Credit: NASA /ESA, A.Feild /STScI

Using NASA’s Hubble Space Telescope, astronomers now can precisely measure the distance of stars up to 10,000 light-years away—10 times farther than previously possible.

Astronomers have developed yet another novel way to use the 24-year-old space telescope by employing a technique called spatial scanning, which dramatically improves Hubble's accuracy for making angular measurements.

The technique, when applied to the age-old method for gauging distances called astronomical parallax, extends Hubble's tape measure 10 times farther into space.

"This new capability is expected to yield new insight into the nature of dark energy, a mysterious component of space that is pushing the universe apart at an ever-faster rate," said Noble laureate Adam Riess of the Space Telescope Science Institute (STScI) in Baltimore, Md.

Parallax, a trigonometric technique, is the most reliable method for making astronomical distance measurements, and a practice long employed by land surveyors here on Earth.

The diameter of Earth's orbit is the base of a triangle and the star is the apex where the triangle's sides meet.

The lengths of the sides are calculated by accurately measuring the three angles of the resulting triangle.

Astronomical Parallax works reliably well for stars within a few hundred light-years of Earth.

For example, measurements of the distance to Alpha Centauri, the star system closest to our sun, vary only by one arc second.

This variance in distance is equal to the apparent width of a dime seen from two miles away.

This illustration shows how the precision stellar distance measurements from NASA’s Hubble Space Telescope have been extended 10 times farther into our Milky Way galaxy than possible previously. 

This greatly extends the volume of space accessible to refining the cosmic yardstick needed for measuring the size of the universe. 

This most solid type of measurement is based on trigonometric Parallax, which is commonly used by surveyors. 

Because the stars are vastly farther away than a surveyor's sightline, Hubble must measure extremely small angles on the sky. 

Credit: NASA, ESA, and A. Feild (STScI)

Stars farther out have much smaller angles of apparent back-and-forth motion that are extremely difficult to measure.

Astronomers have pushed to extend the parallax yardstick ever deeper into our galaxy by measuring smaller angles more accurately.

This new long-range precision was proven when scientists successfully used Hubble to measure the distance of a special class of bright stars called Cepheid variables, approximately 7,500 light-years away in the northern constellation Auriga.

The technique worked so well, they are now using Hubble to measure the distances of other far-flung Cepheids.

Such measurements will be used to provide firmer footing for the so-called cosmic "distance ladder."

This ladder's "bottom rung" is built on measurements to Cepheid variables stars that, because of their known brightness, have been used for more than a century to gauge the size of the observable universe.

They are the first step in calibrating far more distant extra-galactic milepost markers such as Type Ia supernovae.

Riess and the Johns Hopkins University in Baltimore, Md., in collaboration with Stefano Casertano of STScI, developed a technique to use Hubble to make measurements as small as five-billionths of a degree.

To make a distance measurement, two exposures of the target Cepheid star were taken six months apart, when Earth was on opposite sides of the sun.

A very subtle shift in the star's position was measured to an accuracy of 1/1,000 the width of a single image pixel in Hubble's Wide Field Camera 3, which has 16.8 megapixels total.

A third exposure was taken after another six months to allow for the team to subtract the effects of the subtle space motion of stars, with additional exposures used to remove other sources of error.

NASA extends space station life to 2024

This December 22, 2013 NASA image shows astronaut Rick Mastracchio (L) participating in the first Expedition 38 spacewalk designed to troubleshoot a faulty coolant pump on the International Space Station

The International Space Station will operate for an additional four years, or until 2024, the US space agency said Wednesday.

"This is a tremendous announcement for us here in the space station world," said William Gerstenmaier, associate administrator for NASA's Human Exploration and Operations Mission Directorate.

The $100 billion orbiting outpost has been operational for 15 years, and had been expected to remain open to global collaborators until 2020.

More than a dozen countries participate in the space station, which has more living space than a six-bedroom house and comes complete with Internet access, a gym, two bathrooms and a host of science experiments.

NASA said the entire lab is the length of a football field (357 feet, 109 meters).

The International Space Station is the largest space lab ever built, some four times bigger than the Russian space station Mir and about five times as large as the US Skylab.

Although it is near weightless in space, the space station has a mass of 924,739 pounds (419,455 kilograms).

It is maintained by a rotating crew of six astronauts and cosmonauts from the United States, Russia, Europe, Canada and Japan.