U.S. President Donald Trump hands the pen to Vice Chairman of the Joint Chiefs of Staff U.S. Air Force General Paul Selva (2nd L) after signing "Space Policy Directive 4", the directive to establish a Space Force as the sixth branch of the Armed Forces, in the Oval Office at the White House in Washington, U.S., February 19, 2019.

White House Senior Advisor Ivanka Trump meets with local high school students involved in robotics competitions during a tour of the Johnson Space Center in Houston, Texas, U.S. September 20, 2018.

U.S. Vice President Mike Pence speaks inside of the Vehicle Assembly Building at Kennedy Space Center, Florida July 6, 2017.

U.S. Vice President Mike Pence poses for a group photograph with NASA's 12 new astronaut candidates at NASA’s Johnson Space Center in Houston, Texas, U.S., June 7, 2017. NASA astronaut candidates, standing from L-R, Robb Kulin, Jonathan Kim, Robert Hines, Warren Hoburg, Matthew Dominick, Kayla Barron, Jessica Watkins, from L-R kneeling, Francisco Rubio, Loral O’Hara, Jasmin Moghbeli, Zena Cardman, and Raja Chari. Bill Ingalls/Courtesy NASA/Handout via REUTERS ATTENTION EDITORS - THIS IMAGE WAS PROVIDED BY A THIRD PARTY. EDITORIAL USE ONLY. MANDATORY CREDIT.

U.S. ?Vice President Mike Pence? reaches out to shake hands with Secretary of State Rex Tillerson after the first meeting of the U.S. National Space Council at the National Air and Space Museum's Udvar-Hazy Center in Chantilly, Virginia, U.S., October 5, 2017.

White House Senior Advisor Ivanka Trump tours the Johnson Space Center in Houston, Texas, U.S., September 20, 2018.

U.S. President Donald Trump displays the "Space Policy Directive 4" after signing the directive to establish a Space Force as the sixth branch of the Armed Forces in the Oval Office at the White House in Washington, U.S., February 19, 2019.

An aide assembles a model of NASA's Space Launch System (SLS) rocket as the stage is set for U.S. President Donald Trump to deliver remarks at a meeting of the National Space Council at the White House in Washington, U.S. June 18, 2018.

White House Senior Advisor Ivanka Trump makes a call to crew members at the International Space Station during a tour of the Johnson Space Center in Houston, Texas, U.S. September 20, 2018.

U.S. Vice President Mike Pence tours the SpaceX hangar at Launch Complex 39-A where the Dragon crew module and Falcon 9 booster rocket are being prepared for a January 2019 launch at Cape Canaveral, Florida, U.S. December 18, 2018.

U.S. ?Vice President Mike Pence? stands for a photo with U.S. Naval Academy midshipmen after convening the first meeting of National Space Council at the National Air and Space Museum's Udvar-Hazy Center in Chantilly, Virginia, U.S., October 5, 2017.

White House Senior Advisor Ivanka Trump, U.S. Senator Ted Cruz (R-TX) and NASA Administrator Jim Bridenstine tour the Johnson Space Center with astronaut Nicole Mann in Houston, Texas, U.S., September 20, 2018. REUTERS/Loren Elliott - RC1368D444F0

In the shadow of the Space Shuttle Discovery, U.S. ?Vice President Mike Pence? delivers remarks before convening the first meeting of National Space Council at the Smithsonian National Air and Space Museum's Udvar-Hazy Center in Chantilly, Virginia, U.S. October 5, 2017.

U.S. President Donald Trump holds a space astronaut toy as he participates in a signing ceremony for Space Policy Directive at the White House in Washington D.C., U.S., December 11, 2017. REUTERS/Carlos Barria

U.S. Vice President Mike Pence greets USAF personnel after the launch of SpaceX Falcon 9 rocket, scheduled to launch a U.S. Air Force navigation satellite, was postponed after an abort procedure was triggered by the onboard flight computer, at Cape Canaveral, Florida, U.S., December 18, 2018.

U.S. President Donald Trump signs an executive order to create the National Space Council, accompanied by former astronauts Buzz Aldrin (2nd-R), Alvin Drew (3rd-R) and Dave Wolf (L) in the Roosevelt room of the White House, in Washington, DC, U.S. June 30, 2017.

U.S. Vice President Mike Pence visits the Kennedy Space Center, Florida July 6, 2017. Seen behind him is the Orion Capsule that will be launched at a future date.

U.S. Vice President Mike Pence talks with SpaceX employees during a tour of the SpaceX hangar at Launch Complex 39-A, where the Dragon crew module and Falcon 9 booster rocket are being prepared for a January 2019 launch at Cape Canaveral, Florida, U.S. December 18, 2018.