12's, as part of its ALSEP, to be left on the Moon by the astronauts. That seismometer was to be calibrated by the impact, after jettison, of the ascent stage of Apollo 13's LM, an object of known mass and velocity impacting at a known location. Other ALSEP experiments on Apollo 13 included a Heat Flow Experiment (HFE), which would involve drilling two holes deep. This was Haise's responsibility; he was also to drill a third hole of that depth for a core sample. A Charged Particle Lunar Environment Experiment (CPLEE) measured the protons and electrons of solar origin reaching the Moon. The package also included a Lunar Atmosphere Detector (LAD) and a Dust Detector, to measure the accumulation of debris. The Heat Flow Experiment and the CPLEE were flown for the first time on Apollo 13; the other experiments had been flown before. To power the ALSEP, the SNAP-27 radioisotope thermoelectric generator (RTG) was flown. Developed by the U.S. Atomic Energy Commission, SNAP-27 was first flown on Apollo 12. The fuel capsule contained about of plutonium oxide. The cask placed around the capsule for transport to the Moon was built with heat shields of graphite and of beryllium, and with structural parts of titanium and of Inconel materials. Thus, it was built to withstand the heat of reentry into the Earth's atmosphere rather than pollute the air with plutonium in the event of an aborted mission. A United States flag was also taken, to be erected on the Moon's surface. For Apollo 11 and 12, the flag had been placed in a heat-resistant tube on the front landing leg; it was moved for Apollo 13 to the Modularized Equipment Stowage Assembly (MESA) in the LM descent stage. The structure to fly the flag on the airless Moon was improved from Apollo 12's. For the first time, red stripes were placed on the helmet, arms and legs of the commander's A7L spacesuit. This was done as, after Apollo 11, those reviewing the images taken had trouble distinguishing Armstrong from Aldrin, but the change was approved too late for Apollo 12. New drink bags that attached inside the helmets and were to be sipped from as the astronauts walked on the Moon were demonstrated by Haise during Apollo 13's final television broadcast before the accident. Apollo 13's primary mission objectives were to: "Perform selenological inspection, survey, and sampling of materials in