SpaceCamp

Four teenagers: Kathryn, Kevin, Rudy, Tish and 12-year-old Max, go to space camp at Kennedy Space Center near Cape Canaveral, Florida for three weeks during the summer to learn about the NASA space program and mimic astronaut training. They meet their instructor Andie Bergstrom, a NASA-trained astronaut who is frustrated that she has not yet been assigned to a shuttle mission. Her bitterness is compounded by the fact that her husband, camp director Zach Bergstrom, is an astronaut who has walked on the moon.
Max befriends a robot named Jinx, which was deemed unsuitable for space work because it overheated and was overly-literal. Max and the robot declare themselves to be "friends forever". Meanwhile, Kevin pursues Kathryn romantically, Rudy shares his wish to open the first fast food franchise on the moon and Tish reveals that despite appearing to be a Valley girl, she is a genius with a photographic memory.
Kathryn and Kevin sneak away for some romance near the launch pad, but Jinx unintentionally gives them away when Andie and Zach discover they are missing. During a confrontation, Andie explains that she believes Kathryn has what it takes to accomplish her ambition, and explains the necessity of the harsh treatment Andie is giving her. While Kathryn vows to improve her performance, Zach's conversation with Kevin is less successful.
Kevin takes out his anger on Max. Upset, Max states "...I wish I was in space...". Jinx overhears and takes what he said literally. The group are allowed to sit in the Space Shuttle Atlantis during a routine engine test. Jinx secretly enters NASA's computer room and triggers a "thermal curtain failure", causing one of the boosters to ignite during the test. In order to avoid a crash, Launch Control is forced to ignite the second booster and launch the shuttle.
The shuttle is not flight ready, has no long range radio and there is not enough oxygen on board to last to the re-entry window at Edwards Air Force Base. Andie takes the shuttle to the partially constructed Space Station Daedalus to retrieve oxygen stored there. Realizing that while they have no voice communications with NASA they do have telemetry, Tish begins using a switch to send a Morse code signal to NASA, but it is not noticed by ground control.
Andie is slightly too big to reach the oxygen cylinders, so Max suits up for an EVA. During a critical moment, Max begins to panic until Kevin, knowing that Max is a fan of Star Wars, begins calling him "Luke", and tells him to "use the Force", which calms him enough that he can complete the mission, allowing Max and Andie to retrieve the containers.
In the shuttle, Rudy attempts to decipher the technical schematics to work out how to feed the oxygen into the shuttle's tanks. His lack of confidence combined with the time pressure frustrates Kathryn, who tries reading the diagram herself and gives Andie instructions that conflict with Rudy's. Andie follows Rudy's correct instructions. Kathryn's self-confidence is shaken as she realizes her interference nearly caused disaster.
The second oxygen container malfunctions, injuring Andie. Unaware of this, Ground Control begins the autopilot sequence to land the shuttle â closing the bay doors and stranding Andie outside. Andie regains consciousness and urges them to leave her and take the re-entry window, as the shuttle does not have enough oxygen to make the next window. Kathryn is unable to make a decision, but Kevin finally shows himself to be the shuttle Commander and overrides the autopilot enabling Max to rescue Andie. Having missed the Edwards re-entry window, the crew comes up with a plan to land at White Sands, New Mexico after Kathryn briefly mentions the 1982 Space Shuttle mission that landed there. Armed with this news, Tish uses Morse Code to signal NASA to let them land there.
At Ground Control, Jinx brings the signal to Zach's attention and they prepare for the White Sands landing. With Andie injured, Kathryn fulfils her role as pilot, but begins fretting and doubting her abilities until Kevin cajoles and teases her into landing the shuttle.

Question: What does tish use to signal nasa?
Answer: Morse code