{"id":13785,"date":"2018-05-23T01:46:56","date_gmt":"2018-05-22T17:46:56","guid":{"rendered":"https:\/\/wp-productionenv-bjg9h2g2bgg5b8aa.southeastasia-01.azurewebsites.net\/news\/replacements-for-grace-gravity-and-climate-satellites-ready-for-launch\/"},"modified":"2018-05-23T01:46:56","modified_gmt":"2018-05-22T17:46:56","slug":"replacements-for-grace-gravity-and-climate-satellites-ready-for-launch","status":"publish","type":"post","link":"https:\/\/starpath.global\/news\/replacements-for-grace-gravity-and-climate-satellites-ready-for-launch\/","title":{"rendered":"Replacements for GRACE gravity and climate satellites ready for launch"},"content":{"rendered":"
\"\"
Artist\u2019s concept of the GRACE-Follow On satellites. Credit: NASA<\/figcaption><\/figure>\n

A pair of European-built, NASA-backed research satellites set for launch Tuesday from California will extend 15 years of global gravity field measurements collected by the GRACE mission before it ended last year, supplying scientists with data to help track the melting of Earth\u2019s ice sheets and chart the impacts of floods and droughts.<\/p>\n

The two new satellites were built as a follow-up to the Gravity Recovery and Climate Experiment, which used two similar spacecraft to measure the tug of gravity around the world from 2002 through 2017.<\/p>\n

\u201cGRACE and GRACE-Follow On are some of NASA\u2019s most unique missions,\u201d said Michael Watkins, GRACE-Follow On science lead and director of NASA\u2019s Jet Propulsion Laboratory. \u201cWhat GRACE has done, and what GRACE-Follow On will do shortly after its launch, is map the Earth\u2019s water in motion.<\/p>\n

\u201cWhat\u2019s fascinating about GRACE is it does it not by looking the surface of Earth \u2014 not by looking at water or by bouncing a radar off the water \u2014 but by actually measuring the weight of the water,\u201d Watkins said. \u201cSo it actually is able to tell how much water is in a given location on the Earth and how that\u2019s changing over time.\u201d<\/p>\n

The GRACE-Follow On research craft will ride into orbit Tuesday from Vandenberg Air Force Base, California, aboard a SpaceX Falcon 9 rocket, along with five Iridium communications satellites.<\/p>\n

Liftoff from Space Launch Complex 4-East at Vandenberg, a military base around 140 miles (225 kilometers) northwest of Los Angeles, is scheduled for 12:47 p.m. PDT (3:47 p.m. EDT; 1947 GMT).<\/p>\n

On Tuesday\u2019s mission, the Falcon 9 rocket is set to deliver the Iridium and GRACE-Follow On payloads to two different orbits, utilizing two firings of the upper stage\u2019s Merlin engine.<\/p>\n

The GRACE-Follow On satellites will deploy first from the Falcon 9 rocket around 11 minutes after liftoff in an orbit around 304 miles (490 kilometers) above Earth inclined at an angle of 89 degrees to the equator, a track that will take the twin spacecraft almost directly over the poles on each lap around the planet.<\/p>\n

A brief restart of the upper stage engine is planned approximately 57 seconds after liftoff to reach a slightly higher orbit around 373 miles (600 kilometers) in altitude, followed by release of the five Iridium Next satellites one-at-a-time.<\/p>\n

The Iridium satellites will join the company\u2019s network of voice and data relay stations. Iridium\u2019s fleet is being replaced with new-generation satellites offering the company\u2019s one million subscribers improved service, and the upgraded constellation will have 55 spacecraft in orbit with Tuesday\u2019s launch, with 20 more satellites set to go into space in the next few months.<\/p>\n

SpaceX\u2019s launch team conducted a pre-launch hold-down firing of the Falcon 9 rocket Friday at Vandenberg, then returned the launcher to a nearby hangar, where ground crews mated the Iridium and GRACE-Follow On satellites.<\/p>\n

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This image shows the two GRACE-Follow On satellites mounted atop five Iridium communications spacecraft before their attachment to SpaceX\u2019s Falcon 9 rocket. Credit: Iridium<\/figcaption><\/figure>\n

SpaceX does not plan to recover the first stage booster on Tuesday\u2019s mission, but the company could attempt to retrieve part of the Falcon 9\u2019s payload shroud, which shields the satellites during liftoff, then is designed to descend back to Earth with the aid of a parafoil and steering thrusters.<\/p>\n

SpaceX\u2019s fast-moving boat fitted with a net to catch the fairing has been dispatched from the Port of Los Angeles, presumably toward the downrange zone where the fairing is projected to fall.<\/p>\n

Built by Airbus Defense and Space, the identical GRACE-Follow On satellites carry microwave ranging instruments to measure the separation between the craft as they fly around 137 miles (220 kilometers) apart in orbit.<\/p>\n

\u201cThink of the actual satellite size as about the size of a sports car, one in Los Angeles and one in San Diego,\u201d said Phil Morton, NASA\u2019s GRACE-Follow On project manager at JPL. \u201cThat\u2019s about how far apart they\u2019re flying typically.\u201d<\/p>\n

The ranging sensors require exacting precision, with the capability of measuring distance changes between the formation-flying satellites as small as a few microns \u2014 about the width of a blood cell.<\/p>\n

Changes in the range between the two GRACE-Follow On satellite will be caused by tiny variations in the pull of gravity from Earth below, telling scientists about the mass of water, rock and ice around the world.<\/p>\n

\"\"
The GRACE-Follow On satellites during their assembly at Airbus Defense and Space in Friedrichshafen, Germany. Credit: NASA\/Airbus<\/figcaption><\/figure>\n

The 15-year GRACE mission ended last year, and both satellites have re-entered Earth\u2019s atmosphere and burned up after outliving their originally planned five-year lifetimes. They provided the most detailed measurements of how much ice is melting in Greenland and Antarctica, and they monitored how extreme events like floods and droughts \u2014 and normal seasonal changes \u2014 affected the water table and aquifers on Earth\u2019s land masses.<\/p>\n

\u201cWater takes many different forms,\u201d Watkins said. \u201cSometimes it\u2019s in the form of ground water deep underground, sometimes it\u2019s in the form of polar ice gaps, sometimes it can be in the form of ocean water moving around.<\/p>\n

\u201cGRACE observed all of that complete water cycle of the Earth, and how it changes over time \u2026 We have 15 years of GRACE data, and what GRACE has shown is there are significant changes in each part of the world, and how much water is stored in each part of the world.\u201d<\/p>\n

Frank Webb, GRACE-Follow On project scientist at JPL, said the GRACE mission showed Greenland has been losing 281 gigatons of ice per year. A gigaton is roughly equivalent to a cubic kilometer of water, Webb said.<\/p>\n

In Antarctica, ice is melting at an overall average rate of about 120 gigatons per year, with some parts of the continent losing more ice and other regions adding ice.<\/p>\n

From the ice loss in Greenland and Antarctica alone, sea levels are rising by about a millimeter per year, Webb said. Other drivers cause the mean sea level to rise more.<\/p>\n

\u201cI think the rate at which the polar caps were losing mass was something that was a little surpring to folks,\u201d Watkins said. \u201cWhen we launched GRACE (in 2002), it wasn\u2019t clear how fast the polar sheets were changing. I think GRACE gave the first clear picture of what\u2019s going on, and that\u2019s been followed up with other more precise measurements for local areas like with radar or the upcoming ICESat 2 mission.\u201d<\/p>\n

The GRACE-Follow On satellites each weigh around 1,300 pounds, or 600 kilograms, and are sized and shaped the same as the original GRACE spacecraft, ensuring they collect the same types of data.<\/p>\n

\"\"
This map shows trends recorded by the GRACE satellites during its 15-year mission, with regions colored in red losing mass, and regions in green adding mass. Credit: NASA\/GFZ<\/figcaption><\/figure>\n

But engineers added upgrades to the new satellites, including laser ranging devices that the GRACE-Follow On mission will demonstrate in space. The lasers could be capable of measuring the distance between the satellites with a precision 10 times better than the baseline microwave instrument, according to Frank Flechtner, GRACE-Follow On project manager at GFZ in Potsdam, Germany.<\/p>\n

The GRACE-Follow On satellites also carry instruments to signals from GPS navigation satellites that pass through the atmosphere on Earth\u2019s horizon \u2014 as seen from orbit. Scientists can analyze how atmospheric particles altered the GPS radio signal, and use that information to derive estimates of atmospheric temperature and humidity at high altitudes.<\/p>\n

But the $520 million mission\u2019s prime research objective is focused on gravity measurements and Earth\u2019s water cycle.<\/p>\n

\u201cThe satellites are sensitive to all mass change around the globe,\u201d Webb said. \u201cWe make measurements every 30 days, so we see atmospheric, ocean tides, solid earth changes, water ice moving around.\u201d<\/p>\n

Like their predecessors, the new GRACE satellites are designed for five-year lifetimes, but they could last much longer. The additional data will help scientists \u201cunderstand if these trends are just short-term variability, or longer trends related to our evolving climate,\u201d Webb said.<\/p>\n

For example, the original GRACE satellites detected a depletion of water from an aquifer under California during a long-term drought.<\/p>\n

\u201cAt the end of the GRACE time series, we had a large rainstorm, and there was some recovery in the amount of mass \u2014 the amount of water in the ground,\u201d Webb said Monday. \u201cAnd it remains to be seen, since GRACE ended in 2017, how that recovery goes forward. Once GRACE (Follow-On) launches tomorrow, we\u2019ll start getting data, and we\u2019ll have about a one-year gap, and we\u2019ll be able to see how much of that water that fell in precipitation in California actually stayed in the ground and went into storage, and how much actually ran off and went into the ocean.\u201d<\/p>\n

Information about the health and capacity of aquifers will help policymakers, farmers and environmental scientists work together to better manage resources, Webb said.<\/p>\n

\"\"
Michael Watkins, GRACE-Follow On science lead and director of JPL, talks about the mission. Credit: NASA\/Joel Kowsky<\/figcaption><\/figure>\n

The GRACE-Follow On satellites were supposed to launch on a Dnepr rocket from Russia last year, but the Russian government decided to discontinue the Dnepr program \u2014 managed by a Russian-Ukrainian company called Kosmotras \u2014 after relations deteriorated with Ukraine, where the launcher was manufactured.<\/p>\n

The selection of a rocket was the responsibility of GRACE-Follow On\u2019s German team, and GFZ arranged for another launch opportunity with Iridium and SpaceX when it was clear the original Dnepr launch contract would not be fulfilled.<\/p>\n

Iridium already had a contract with SpaceX for seven Falcon 9 flights, each with 10 Iridium satellites on-board, to build out the company\u2019s new-generation telecom network. Iridium agreed to reserve an eighth launch in a rideshare arrangement with GFZ, carrying just five Iridium satellites to account for the extra capacity needed by the two GRACE Foll0w-On spacecraft.<\/p>\n

Iridium also had planned two launch its first two new-generation satellites on a Dnepr rocket, but like in GRACE Follow-On\u2019s case, that agreement was blocked by the cancellation of the Dnepr program.<\/p>\n

\u201cWe were thinking we\u2019d use the Dnepr rocket for two, and when that wasn\u2019t going to work out because the Russians weren\u2019t going to fly it, we still wanted to launch a few more satellites,\u201d said Matt Desch, Iridium\u2019s CEO, in an interview with Spaceflight Now. \u201cTalking to SpaceX and asking what they would recommend \u2026 they pointed us initially toward GRACE because GRACE also had been looking for a ride.<\/p>\n

\u201cSo we took the lead on it,\u201d Desch said. \u201cWe thought that this would make a lot of sense. We reached out to GRACE directly, we started talking to people at JPL, GFZ, and started talking about the details of it. We contracted with SpaceX, and then we kind of subcontracted with GRACE to use half the payload capacity, and started working out the technical details well over a year ago.\u201d<\/p>\n

The marriage of the Iridium satellites, built by a partnership of Thales Alenia Space and Orbital ATK, and the Airbus-based GRACE Follow-On satellites, with a SpaceX Falcon 9 rocket was a good example of global cooperation between parties which are sometimes competitors, Desch said.<\/p>\n

Email the author.<\/i><\/b><\/p>\n

Follow Stephen Clark on Twitter: @StephenClark1.<\/strong><\/em><\/p>\n","protected":false},"excerpt":{"rendered":"

Artist\u2019s concept of the GRACE-Follow On satellites. Credit: NASA A pair of European-built, NASA-backed research satellites set for launch Tuesday from California will extend 15 years of global gravity field measurements collected by the GRACE mission before it ended last year, supplying scientists with data to help track the melting of Earth\u2019s ice sheets and […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"","ping_status":"","sticky":false,"template":"","format":"standard","meta":{"_acf_changed":false,"inline_featured_image":false,"footnotes":"","_links_to":"","_links_to_target":""},"categories":[2],"tags":[1657,291,159,479,2957,2947,530,2193],"class_list":["post-13785","post","type-post","status-publish","format-standard","hentry","category-news","tag-airbus-defense-and-space","tag-commercial-space","tag-earth-observation","tag-falcon-9","tag-gfz","tag-grace-fo","tag-iridium","tag-iridium-next"],"acf":[],"_links":{"self":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/13785"}],"collection":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/comments?post=13785"}],"version-history":[{"count":0,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/posts\/13785\/revisions"}],"wp:attachment":[{"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/media?parent=13785"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/categories?post=13785"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/starpath.global\/blog\/wp-json\/wp\/v2\/tags?post=13785"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}