diff --git a/crates/physics/apsis-frames/src/earth_rotation.rs b/crates/physics/apsis-frames/src/earth_rotation.rs
index 262c11e..31eec1b 100644
--- a/crates/physics/apsis-frames/src/earth_rotation.rs
+++ b/crates/physics/apsis-frames/src/earth_rotation.rs
@@ -1,7 +1,6 @@
 //! The Earth Rotation Angle and the rotation it defines between the
 //! inertial and Earth-fixed frames.
 
-use crate::frame::{Ecef, Eci};
 use apsis_math::Mat3;
 use core::f64::consts::PI;
 
@@ -125,19 +124,3 @@ pub fn rotation_eci_to_ecef(angle: EarthRotationAngle) -> Mat3 {
 pub fn rotation_ecef_to_eci(angle: EarthRotationAngle) -> Mat3 {
     rotation_eci_to_ecef(angle).transpose()
 }
-
-impl Eci {
-    /// Converts this inertial vector to the Earth-fixed frame at the given
-    /// Earth Rotation Angle.
-    pub fn to_ecef(self, angle: EarthRotationAngle) -> Ecef {
-        Ecef::new(rotation_eci_to_ecef(angle) * self.0)
-    }
-}
-
-impl Ecef {
-    /// Converts this Earth-fixed vector to the inertial frame at the given
-    /// Earth Rotation Angle.
-    pub fn to_eci(self, angle: EarthRotationAngle) -> Eci {
-        Eci::new(rotation_ecef_to_eci(angle) * self.0)
-    }
-}
diff --git a/crates/physics/apsis-frames/src/frame.rs b/crates/physics/apsis-frames/src/frame.rs
deleted file mode 100644
index cccda08..0000000
--- a/crates/physics/apsis-frames/src/frame.rs
+++ /dev/null
@@ -1,41 +0,0 @@
-//! Frame marker types.
-
-use apsis_math::Vec3;
-
-/// A position or vector expressed in the Earth-centered inertial frame.
-///
-/// The frame is aligned with the mean equator and equinox of J2000.0. It is
-/// treated as inertial here, so it does not rotate with the Earth.
-#[derive(Debug, Clone, Copy, PartialEq)]
-pub struct Eci(pub Vec3);
-
-/// A position or vector expressed in the Earth-centered Earth-fixed frame.
-///
-/// The frame rotates with the Earth, so a point fixed to the ground has
-/// constant coordinates in it.
-#[derive(Debug, Clone, Copy, PartialEq)]
-pub struct Ecef(pub Vec3);
-
-impl Eci {
-    /// Creates an inertial frame vector from its components.
-    pub const fn new(vector: Vec3) -> Self {
-        Self(vector)
-    }
-
-    /// Returns the underlying vector.
-    pub const fn vector(self) -> Vec3 {
-        self.0
-    }
-}
-
-impl Ecef {
-    /// Creates an Earth-fixed frame vector from its components.
-    pub const fn new(vector: Vec3) -> Self {
-        Self(vector)
-    }
-
-    /// Returns the underlying vector.
-    pub const fn vector(self) -> Vec3 {
-        self.0
-    }
-}
diff --git a/crates/physics/apsis-frames/src/lib.rs b/crates/physics/apsis-frames/src/lib.rs
index 8f92d15..b90b91f 100644
--- a/crates/physics/apsis-frames/src/lib.rs
+++ b/crates/physics/apsis-frames/src/lib.rs
@@ -1,8 +1,11 @@
-//! Reference frame definitions and the transformations between them.
+//! Reference frame definitions and the rotation between the inertial and
+//! Earth-fixed frames.
 //!
 //! A reference frame fixes the orientation and origin that a vector is
-//! expressed relative to. This crate defines the two frames used for
-//! near-Earth work and the rotation between them.
+//! expressed relative to. This crate names the two frames used for
+//! near-Earth work and computes the rotation between them. Concrete
+//! position types that carry a frame are defined in `apsis-coord`; this
+//! crate works with the rotation matrix and the angle that defines it.
 //!
 //! The inertial frame is the Earth-centered inertial (ECI) frame aligned
 //! with the mean equator and equinox of J2000.0. Its axes are fixed in
@@ -11,16 +14,16 @@
 //!
 //! The rotating frame is the Earth-centered Earth-fixed (ECEF) frame. Its
 //! third axis is the Earth's rotation axis and its first axis follows the
-//! prime meridian, so a point fixed to the ground has constant
-//! coordinates in it.
+//! prime meridian, so a point fixed to the ground has constant coordinates
+//! in it.
 //!
 //! The two are related by a rotation of [`EarthRotationAngle`] about the
-//! common third axis. This crate models the Earth's rotation with the
-//! Earth Rotation Angle, which is a function of UT1 only. It does not
-//! apply precession or nutation, because an angle accurate to a few
-//! hundredths of a degree is sufficient for pointing and coverage work and
-//! the full model needs the orientation of the celestial pole, which is a
-//! separate computation.
+//! common third axis. This crate models the Earth's rotation with the Earth
+//! Rotation Angle, which is a function of UT1 only. It does not apply
+//! precession or nutation, because an angle accurate to a few hundredths of
+//! a degree is sufficient for pointing and coverage work and the full model
+//! needs the orientation of the celestial pole, which is a separate
+//! computation.
 //!
 //! Source: the Earth Rotation Angle expression is from the International
 //! Astronomical Union, as given in the *IERS Conventions (2010)*, equation
@@ -43,10 +46,8 @@
 #![deny(missing_docs)]
 
 mod earth_rotation;
-mod frame;
 
 pub use earth_rotation::{
     ERA_J2000_TURNS, ERA_RATE_TURNS_PER_DAY, EarthRotationAngle, rotation_ecef_to_eci,
     rotation_eci_to_ecef, ut1_days_from_j2000,
 };
-pub use frame::{Ecef, Eci};
diff --git a/crates/physics/apsis-frames/tests/earth_rotation.rs b/crates/physics/apsis-frames/tests/earth_rotation.rs
index 492f774..75296d3 100644
--- a/crates/physics/apsis-frames/tests/earth_rotation.rs
+++ b/crates/physics/apsis-frames/tests/earth_rotation.rs
@@ -1,8 +1,8 @@
 //! Tests for the Earth Rotation Angle and the frame rotations.
 
 use apsis_frames::{
-    ERA_RATE_TURNS_PER_DAY, EarthRotationAngle, Ecef, Eci, rotation_ecef_to_eci,
-    rotation_eci_to_ecef, ut1_days_from_j2000,
+    ERA_RATE_TURNS_PER_DAY, EarthRotationAngle, rotation_ecef_to_eci, rotation_eci_to_ecef,
+    ut1_days_from_j2000,
 };
 use apsis_math::Vec3;
 use core::f64::consts::PI;
@@ -125,38 +125,6 @@ fn rotation_carries_the_second_axis_toward_the_first() {
     assert!((rotated.norm() - 1.0).abs() < EPS);
 }
 
-#[test]
-fn frame_conversions_round_trip() {
-    let angle = EarthRotationAngle::from_ut1_days(9.25);
-    let original = Eci::new(Vec3::new(7_000.0, -1_500.0, 3_200.0));
-    let ecef = original.to_ecef(angle);
-    let back = ecef.to_eci(angle);
-    assert!((back.vector() - original.vector()).norm() < 1e-9);
-}
-
-#[test]
-fn frame_conversion_preserves_length() {
-    let angle = EarthRotationAngle::from_ut1_days(-3.5);
-    let vector = Vec3::new(6_878_137.0, 0.0, 0.0);
-    let converted = Eci::new(vector).to_ecef(angle);
-    assert!((converted.vector().norm() - vector.norm()).abs() < 1e-6);
-}
-
-#[test]
-fn rotating_background_returns_a_ground_point_to_the_same_longitude() {
-    // A point on the equator at zero longitude in the Earth-fixed frame is
-    // rotated by minus the Earth Rotation Angle in the inertial frame.
-    let angle = EarthRotationAngle::from_ut1_days(1.5);
-    let ground = Ecef::new(Vec3::new(6_378_137.0, 0.0, 0.0));
-    let inertial = ground.to_eci(angle);
-    let expected = Vec3::new(
-        6_378_137.0 * angle.radians_positive().cos(),
-        6_378_137.0 * angle.radians_positive().sin(),
-        0.0,
-    );
-    assert!((inertial.vector() - expected).norm() < 1e-6);
-}
-
 #[test]
 fn a_full_turn_returns_to_the_same_rotation() {
     // The rotation depends on the angle modulo one turn, so angles that
diff --git a/crates/physics/apsis-frames/tests/frame.rs b/crates/physics/apsis-frames/tests/frame.rs
deleted file mode 100644
index 7e61136..0000000
--- a/crates/physics/apsis-frames/tests/frame.rs
+++ /dev/null
@@ -1,19 +0,0 @@
-//! Tests for the frame marker types.
-
-use apsis_frames::{Ecef, Eci};
-use apsis_math::Vec3;
-
-#[test]
-fn wrappers_preserve_the_vector() {
-    let vector = Vec3::new(1.0, 2.0, 3.0);
-    assert_eq!(Eci::new(vector).vector(), vector);
-    assert_eq!(Ecef::new(vector).vector(), vector);
-}
-
-#[test]
-fn wrappers_compare_by_value() {
-    let vector = Vec3::new(-4.0, 5.5, 0.0);
-    assert_eq!(Eci::new(vector), Eci(vector));
-    assert_eq!(Ecef::new(vector), Ecef(vector));
-    assert_ne!(Eci::new(vector), Eci::new(Vec3::ZERO));
-}